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Rhubarb Custard – Crustless or Crisp

Rhubarb Custard – Crustless or Crisp
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Rhubarb season is brief and there are so many delicious sweet and savory rhubarb dishes to make. This tangy-sweet custard can be enjoyed as a simple custard or as a rhubarb crisp. It is a rich vanilla custard over a layer of tart rhubarb and sprinkled with a nutty streusel topping. It is also easily modified to low carb without a loss in flavor.

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Rhubarb custard with low carb nut crisp topping
Rhubarb custard with low carb nut crisp topping
Rhubarb custard with no crust
Rhubarb custard with no crust

Is Rhubarb a Fruit or Vegetable?

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

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 custard laid out in bowls.
Ingredients for rhubarb custard

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 part, it 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.

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, 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.

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.

Getting the Custard to Set without a Water Bath?

Rhubarb custard in parfait glass.
Rhubarb custard parfait

While some custards do better cooked in a waterbath, this rhubarb custard dish is easy and successfully sets without a hot-water bath, but there are 3 key considerations:

  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

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.

Crustless Rhubarb Custard

Rhubarb custard with no crust
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)
4.6 from 15 votes
Prep Time 10 mins
Cook Time 30 mins
Servings 9
Calories 269


  • 6-8 ramekins or 9” baking dish (see notes)
  • sharp knife
  • medium size bowl



  • 1 ½ lb rhubarb cut into 1/2” pieces (about 3-4 cups)
  • 1 cup sugar divided; also Include extra 1-2 Tablespoons sugar to sprinkle over top
  • 4 medium eggs
  • ½ Cup water
  • 1 cup fluid heavy whipping cream
  • ¼ Cup butter
  • 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 substitute I used Truvia
  • ½ cup nuts chopped finely (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.
  • 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.
  • 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, and bake at 350° F for about 35 minutes. It should jiggle slightly on the top and be at least 175°F
    If adding the crisp topping, prepare it as in the direction below and sprinkle over the rhubarb custard mixture before baking.
  • To get a deeper custard, distribute rhubarb into a 9” pie plate and pour custard over the top. Bake at 350°F for 1 hour. It should jiggle on top and be at least 175°F
    If adding the crisp topping, prepare it as in the direction below and sprinkle over the rhubarb custard mixture before baking.
  • 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)



** 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.
** 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
Did you make this recipe?If you tried this recipe, please give it a 5-star rating! To do this, just click on the stars above. And don’t forget to tag me at @dorothy_stainbrook_heathglen, if you share a picture on Instagram! You can also tag me at #heathglen!
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Wednesday 8th of June 2022

just wondering what is a sharb knife ?

dorothy stainbrook

Wednesday 8th of June 2022

Haha, you caught me! I have come to rely on spell check so I didn’t catch that. I wonder why spell check didn’t? Sharb must be a word. Anyway….supposed to be sharp!


Sunday 8th of May 2022

Recipe didn't say what size baking dish to use, I used a 9x9 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 ramekins

dorothy stainbrook

Saturday 14th of May 2022

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.

dorothy stainbrook

Sunday 8th of May 2022

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.


Monday 31st of May 2021

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.

dorothy stainbrook

Tuesday 1st of June 2021

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?


Friday 28th of May 2021

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! :)

dorothy stainbrook

Friday 28th of May 2021

Haha yes they taste pretty much the same but the green variety looks pretty awful in desserts!

Christiane Elliott

Friday 28th of May 2021

Hi, 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

dorothy stainbrook

Friday 28th of May 2021

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.

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