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Rhubarb Custard with Nut Streusel Topping: No Water Bath

Rhubarb Custard with Nut Streusel Topping: No Water Bath
Home » Seasonal Recipes » Spring » Rhubarb Custard with Nut Streusel Topping: No Water Bath

Rhubarb season is brief and there are so many delicious sweet and savory rhubarb dishes to make. This tangy-sweet dish can be enjoyed as a sweet-tart custard or as a sweeter rhubarb crisp.

I’ve also added whipped cream to the leftovers and made it into an adapted “Eton Mess”. Try it in all three versions!

3 white ramekins of rhubarb crisp on a red mat.
3 ramekins of rhubarb custard
Rhubarb crisp in a white pie plate on a red mat.
Low Carb Rhubarb Crisp

Jump to: RECIPE | All About Rhubarb | Illustrated Step by Step | Setting a Custard without Water Bath

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All About Rhubarb

Is Rhubarb a Fruit or Vegetable?

For a little background, rhubarb is a vegetable that is often used like a fruit in cooking, Rhubarb has pink to red celery-like stalks and large green leaves.

The only part of the rhubarb plant that is edible is the stalk; the leaves are toxic and must be removed and discarded.

The tart-flavored stalks are always served sweetened and cooked. Field-grown rhubarb is available April through July, while hothouse varieties are sold January through June.

Red rhubarb growing in the soil in a garden.
Red rhubarb in the garden

What to Look for when Purchasing:

  • Look for bunches of rhubarb with crisp, straight well-colored stalks. Any attached leaves should look fresh, although they should never be eaten, as they are toxic. Most stores and markets have cut off the leaves.
  • Avoid rhubarb with stalks that are turning green or have blemishes or cuts.

How to Store and Freeze Rhubarb

  • Refrigerate unwashed rhubarb in a plastic bag for 3 to 5 days.
  • Freeze fresh, cut-up rhubarb in freezer-weight plastic bags for up to 9 months.

How to Prepare Rhubarb for Cooking:

  • Trim off and discard all leaves and the ends of the stalks.
  • Remove any brown spots or coarse strings with a vegetable peeler. Wash under cold running water.
  • Cut the stalks crosswise into 1- to 2-inch pieces if using in a sauce or compote. Because it breaks down easily during cooking, rhubarb is usually not cut into small pieces. For this custard recipe however, I have cut the rhubarb into smaller 1/2” pieces.

Ingredients for Rhubarb Custard:

An ingredient list and detailed directions are listed in the recipe card below. Here is a photo of all the ingredients you need measured out in the precise amounts:

Ingredients for rhubarb crisp laid out in bowls on a cutting board.
Ingredients for Low Carb Rhubarb Crisp

Illustrated Step by Step

Step #1: Cut rhubarb into small pieces and sprinkle with sugar and set aside.

Bowl of rhubarb cut into small pieces and sprinkled with sugar.
Step #1

Step #2: In a stand mixer, blend eggs, sugar, water, cream, butter, sale, vanilla, cornstarch and orange zest

Stand mixer bowl of egg custard mixture.
Step #2

Step #3: In a food processor, mix flour, sugar, cinnamon, nuts, butter and salt until crumbly

Food processor with almond flour, sugar and butter ready to mix into crumble topping.
Step #3

Step #4: Layer the rhubarb in the baking dish, pour over the custard mixture and top with the crumble topping.

Baking dish with cut up rhubarb, food processor bowl of crumble topping, and bowl of custard mixture.
Step #4

Step #5: Bake rhubarb crisp at 350 F for about 40 minutes.

Rhubarb crisp in a white baking dish on a cutting board, ready for the oven.
Step #5

How to Modify Rhubarb Custard & Crisp to Low Carb:

Rhubarb custard and rhubarb custard crisp can easily be modified to be low carb recipes.

For the crisp:

Modifying the “crisp” to be low carb is a matter of switching white enriched flour to almond flour and switching pure cane sugar to a sugar substitute. Use nuts instead of oats for the desired crunch in a crisp.

For the Custard:

Custards include eggs, cream and sugar. Eggs and cream are staples on a low carb or keto diet so for the custard, it is mostly a matter of switching out the sugar to a sugar substitute.

My favorite sugar substitute is A monkfruit blend. The monkfruit blends usually include erythritol. The flavor of the custard using this blend is very good.

Some people will notice a “cooling” taste from the erythritol part of the blend. Some people also experience digestive issues with erythritol.

Even though erythritol sounds like an artificial compound however, it occurs naturally in a variety of foods (e.g., grapes, mushrooms, pears and watermelon) and some fermented foods and beverages like beer, cheese, sake, soy sauce and wine.

Erythritol is produced using fermentation.

For the Thickener:

Cornstarch is often used to thicken fruit pies, and this would include a rhubarb pie. While cornstarch is not low carb, you don’t usually use enough of it to make much of a difference.

Eton Mess Recipe for the Leftovers

Eton mess is a classic British dessert made of a mixture of fresh fruit, cream and crushed baked meringue. It’s deliciously simple and perfect for lazy summer days.

The recipe below for the rhubarb crisp makes a fairly large crisp and if you don’t eat it fairly quickly, the custard will start to weep as it gets warm.

Since there is just 2 people in our current household, I decided to change up the leftover custard as it softened.

Basically I just scooped up the crisp/custard into a dish and added some whipped cream. It looked like an eton mess to me, with the crumble crust acting as the meringue.

Granted it is an adaptation of the classic eton mess dessert, but I must say it was a delicious adaptation!

Rhubarb custard with crisp topping and layered with whipped cream and topped with tarragon.
Adapted version of Eton Mess: rhubarb custard, mixed up with nut crumble and whipped cream

Getting Custard to Set without a Water Bath

While some custards do better cooked in a water-bath, this rhubarb custard dish is easy and successfully sets without a hot-water bath.

Here are the 3 key considerations when getting the custard to set:

  1. You need to match the size of the baking dish to the length of cooking time. If you use shallow baking dishes (i.e., 8 ramekins or a 1” pie plate) the custard will set in about 35 minutes. In a 9” pie plate it took 1 hour before it was properly set. It should be a bit jiggly when you shake it and have an internal temperature of 175 F or more.
  2. You need to use a little flour or a little cornstarch in the custard mix. Both of them will work, but I used 2 Tablespoon flour in the first batch, and 1 Tablespoon cornstarch in the second batch. I prefer the set with the cornstarch, but it is a little higher in carbs.
  3. Let the custard cool completely when removed from oven. Then refrigerate (covered) to keep the custard from becoming runny.

Flour vs Cornstarch as Thickener for Custards

Either Flour or cornstarch can be used as a thickener for custards. They are different however.

Here are a few key distinctions to be aware of:

  • You can’t use cornstarch instead of flour at a 1:1 ratio. You will need to use twice as much flour as cornstarch (or a ratio of 2:1)
  • Flour will start to thicken at a lower temperature, but it needs to be cooked long enough to get the taste out (at least 20 minutes). Cornstarch, on the other hand, doesn’t have a taste but you need to get the temperature up to almost boiling before it reaches it’s thickening power.
  • They have a different look in dishes. Cornstarch will have a slight shine and be transparent. Flour will be more opaque. For this reason a lot of cooks use cornstarch for sweet dishes and flour for savory type sauces.
  • Flour has more nutrients and less carbs than cornstarch

Testing Results:

I tested this recipe using 2 Tablespoons flour for the first batch and 1 Tablespoon cornstarch for the second batch.

I prefer the custard to be a bit thicker and found that the cornstarch worked better for me. If I were to make this again with flour, I would try 3 Tablespoons rather than 2.

Neither cornstarch or flour will have a taste in this recipe, as it does cook long enough at a high enough temperature to erase the taste of the flour.

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Crustless Rhubarb Custard

3 white ramekins of rhubarb crisp on a red mat.
This rhubarb custard can be enjoyed on it’s own as a creamy sweet-tart dessert, or you can add a low carb nut topping to it and enjoy it as a crisp (recipe for crisp topping included)
4.67 from 21 votes
Prep Time 10 minutes
Cook Time 30 minutes
Servings 9
Calories 269




  • 1 ½ lb rhubarb (cut off ends before weighing) cut into 1/2” pieces (about 5-6 cups)
  • 1 /2 cup sugar Plus a couple of tablespoons to sprinkle over the top
  • 4 medium eggs
  • ½ Cup sugar
  • ½ Cup water
  • 1 cup fluid heavy whipping cream
  • ¼ Cup butter cold
  • 1 Tablespoon Cornstarch Alternatively use 2-3 Tablespoons flour
  • ¼ Teaspoon salt
  • 1 tsp vanilla
  • 1 Tablespoon zest from 1 orange

For the Crisp Topping

  • 1 Cup almond flour
  • 1 cup brown sugar Or brown sugar substitute
  • ½ cup nuts chopped (I used pecans)
  • ½ tsp cinnamon
  • ¼ tsp salt
  • 4 oz unsalted butter chilled and cut into small pieces
  • 1-2 Tbsp Fresh tarragon chopped ** optional


  • Preheat oven to 350° F.
    In a large bowl, mix together cut-up rhubarb, 1/2 cup sugar (or sugar substitute) and set aside.
    1 1/2 lb rhubarb (cut off ends before weighing), 1 /2 cup sugar
  • In a mixer, beat together until well combined the eggs, the other 1/2 cup sugar, water, cream, butter, 1 cornstarch, salt, vanilla and orange zest.
    4 medium eggs, 1/2 Cup water, 1 cup fluid heavy whipping cream, 1/4 Cup butter, 1 Tablespoon Cornstarch, 1/4 Teaspoon salt, 1 tsp vanilla, 1 Tablespoon zest from 1 orange, 1/2 Cup sugar
  • Distribute the rhubarb evenly into 6-8 ramekins until they are about 3/4 full. I used 8 ramekins that were 5” diameter by 1 1/2 inch deep.
    Distribute rhubarb into a 10” shallow single baking dish I made it in a 10” diameter round baking dish which was 1 1/2” deep
    Pour egg/cream mixture over the top of the rhubarb. If adding the crisp topping, prepare it as in the direction below and sprinkle over the rhubarb custard mixture at this point before baking.
    Bake at 350° F for about 35 minutes if in a shallow baking dish. It should jiggle slightly on the top and be at least 175°F internal temperature
    **Note: To get a deeper custard, distribute rhubarb into a 9” pie plate instead of a 10 “ dish and bake at 350°F for 1 hour. It should jiggle on top and be at least 175°F internal temp.
  • Let the custard cool completely, and then place in refrigerator to keep custard from becoming runny. You can cover with plastic wrap, aluminum foil or a plate before placing in refrigerator.
  • To make the crisp topping: Add all ingredients except the butter to a food processor and pulse until blended. Then add the chilled butter (cut up into small chunks) to the processor and pulse for a minute or until the mixture is crumbly and well blended (like a coarse meal).
    Sprinkle the crisp topping over the rhubarb mixture and add the chopped tarragon if you are using that option, and bake at 350° F.
    Check on the crisp at 30 minutes and watch until it is browned to your liking. Make sure the custard is done underneath the topping (175° F)
    1 Cup almond flour, 1 cup brown sugar, 1/2 cup nuts, 1/2 tsp cinnamon, 1/4 tsp salt, 4 oz unsalted butter, 1-2 Tbsp Fresh tarragon



** This can be made in a single baking dish instead of ramekins but the cooking time will vary.  Cook for 1 hour in a 9” diameter pie plate and about 35 minutes in a 10” circular round baking dish filled it to about 1” deep. The cooking time is dependent on the depth of the custard.
** Use either 2-3 Tablespoons flour or 1 Tablespoon cornstarch for thickener.


Calories: 269kcalCarbohydrates: 27gProtein: 4gFat: 17gSaturated Fat: 10gPolyunsaturated Fat: 1gMonounsaturated Fat: 4gTrans Fat: 1gCholesterol: 116mgSodium: 213mgPotassium: 273mgFiber: 1gSugar: 24gVitamin A: 729IUVitamin C: 6mgCalcium: 99mgIron: 1mg
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  1. williamstevenherz4302 says:

    Our rhubarb plants almost never have any redness in the stalks. This may be because they are in a lot of shade and fairly pitiful specimens. I haven’t ran into problems eating them but we aren’t eating a lot. The toxin in rhubarb is oxalic acid and is probably concentrated mainly in the leaves regardless of stalk color. But oxalic acid is also responsible for the tangy flavor of French sorrel, spinach and kale. You’d probably have eat 10 lbs. of spinach to run into problems, but I suspect there is a lot more in rhubarb and sorrel. Oxalates do damage by producing kidney stones. This isn’t a serious risk for most people in the amounts eaten, although it won’t hurt to drink a glass of water with them. But some people have a predisposition to form kidney stones, and particularly oxalate stones, and need to avoid oxalic acid containing foods altogether.

    • It was always my understanding that it was just the leaves of rhubarb that were toxic. Maybe I’ll do a deeper dive into this based on your comments however. Re the redness of the stalks: it’s variety specific. There are several different varieties of rhubarb ranging from red to speckled to green. Here’s a little paragraph From the link below that talks about varieties:

      “Gardeners and pie makers often assume that deep red rhubarb is the sweetest. However, the color of rhubarb actually has very little to do with its flavor. If you’re a fan of bright red rhubarb, guess what? Rhubarb actually comes in several colors, including pink and speckled rhubarb varieties. You may even discover that green varieties of rhubarb are surprisingly sweet, and tend to be more productive!”

      Read more at Gardening Know How: Rhubarb Varieties: Types Of Rhubarb For The Garden

  2. Alyssa Olson says:

    Can I make the custard in one large dish versus small ramekins? Will this alter the baking time? Thanks!

    • Yes, you can certainly make it in one large dish. It shouldn’t effect baking time, but I would check on it 5 minutes before the end of baking time. It should have a slight jiggle in the middle of the pie but not the outer edges. All ovens are different, so it’s a good practice to check on things around 5 minutes before the end anyway. Let me know how it turns out. 🙂

  3. Dorothy says:

    Anyone have great savory ways to use rhubarb?5 stars

    • LaRoy says:

      @Dorothy, I make a really tasty rhubarb mincemeat(no meat) it makes a delicious pie, tarts and cake. I have to eat gluten free and I love this.

  4. Joli says:

    Picky husband loves this recipe.
    NuTrail makes a granola that is delightful as a topping with two grams carbs per 1/3 cup serving.5 stars

  5. Christiane Elliott says:

    Would you know where the 38 carbs come from? It is awfully high for a low carb recipe.
    And Fiber was only 1 so net carbs would be 37.
    Thank you

    • Hi Christiane, So I went back and look at the nutrition calculator to see where the carbs were coming from. Most of them come from the sugar substitute (I tried the calculator with splenda, monkfruit and then just “sugar substitute”) 1 1/2 cups in the custard and 1/2 cup in the crisp is where the carbs are coming from. Rhubarb is quite sour so you could try and cut back on the sugar substitute, but it might not be as sweet as you want for a dessert. Here is the breakdown for the carbs using the generic word sugar substitute instead of monkfruit: 2.6 from the rhubarb, 34.25 from the sugar substitute, 3 from the almond flour, and 6 from the nuts. Everything else is something under 1. The lowest I could get it was to use a Powdered Sugar Substitute in the calculation which ended up with 33 grams per serving. I guess I would try a different fruit crisp that didn’t require so much sugar substitute to make it a sweet dessert. For me, it is still low “sugar” enough to be an occasional dessert. Another alternative is to just make the custard part and not the crisp on top. That would lower the carb content.

  6. Joan says:

    One year I was given a rhubarb plant for Mother’s Day. For several years I never picked it because it was green and never turned red. Finally, I found out it was of the green rhubarb variety! 🙂

  7. Donna says:

    The custard was delicious. But I cooked it in a pie pan and with the low temperature it took well over an hour and even then was not really firm. Next time I will bake it in ramekins.

    • Thank you for the comment Donna. I’m surprised it didn’t work as well in the pie pan. I wonder if it would have worked better if the temperature was increased to accommodate the larger surface? I’ll try it this year in a pie pan and see what happens with our stove. All stoves are a bit different….maybe yours runs a bit cooler?

  8. Jessica says:

    Recipe didn’t say what size baking dish to use, I used a 9×9 pan and it did not cook well at all. After 40 minutes was still completely liquid. Baked for another 15 and still wasn’t set. Added tinfoil and left for another 10 minutes and then just turned the oven off because I needed to leave. When I came back it was pretty much just custard sitting on top of a bunch of liquid. After microwaving the rhubarb does the liquid need to be strained out?

    I cut back to about 1.25 cups total of sugar and still found it to be pretty sweet. I prefer the tartness of the rhubarb though so could be personal preference. Overall I really like the concept of the recipe, I just wouldn’t say that it can be made in a baking dish instead of ramekins3 stars

    • Hi Jessica, Based on your comments I remade this recipe a couple of times last week. I decreased the sugar like you mentioned and I thought it was better also (thanks). There were 2 things I changed that will make this recipe more successful for people not making it in ramekins:

      1) I added a thickener to the custard mix (I made it once with 3 Tablespoons flour and once with 1 Tablespoon cornstarch and both worked)

      2) I made it in a shallow 10” pie plate and that only took 35 minutes to set at 350 F. I also make it in a 9” pie plate which was deeper and that took 1 hour at 350 F to set.

      3) To be sure if it will set, use a digital thermometer and get it to at least 175 (or more). It should be jiggly on top but not liquid

      4) Make sure and let it cool completely before slicing. Then place in the refrigerator until ready to serve.

      I hope that helps. I updated the recipe to reflect those tests and I appreciate your comments. Always looking to improve these recipes and comments help.

    • Thanks for the specifics in your comment. My rhubarb is just up and I was getting ready to make this again. I’ll test it in a baking pan and see what I get. I did do it in a circular baking dish rather than the ramekins and it came out great (like the photo in the post. Maybe my circular baking dish was more shallow than a 9 x 9.

      It could have something to do with the modification of the sugar that you did. At any rate, I’ll test it and update about the results.

  9. jerilyn says:

    just wondering what is a sharb knife ?

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