Vanilla Rhubarb Custard Bars

For me,the delights of spring can be summed up in one amazing plant: Rhubarb. An often misunderstood plant, rhubarb is an absolutely incredible ingredient in baked goods as its characteristic tart flavor makes it the perfect accent to a variety of sweet desserts. Rhubarb is often dismissed for being simply a pie plant, but its uses extend far beyond this; crisps, muffins, and cakes are just a few examples of the many vehicles featuring this delicious ingredient.

For years, my traditional go-to rhubarb recipe has been Rhubarb Sour Cream Coffeecake. Although this recipe is indeed delicious,  I have recently become interested in using rhubarb in different types of baked goods as a tribute to its great versatility. For my most recent rhubarb experiment I tried my hand at rhubarb cookie bars, and the result was simply incredible!

I found the idea for this recipe on the Land O’Lakes website, a site which contains hundreds of delicious buttery recipes, both savory and sweet. Over the past few years I have made numerous baked goods from this site and the result has always been sensational. And these bars were no different.

Although originally supposed to be a cookie cake, after a few alterations these bars turned out more along the line of custard pie bars, a result which, in my opinion, is all the more welcome! These delectable Vanilla Rhubarb Custard Bars consist of a delicate browned butter shortbread crust nestled underneath a row of sweetened rhubarb and decadent vanilla custard-esque filling.  And to finish, these delicious morsels are adorned with crackly, brown sugar-crusted top.

What words can describe this creation? Just one: Yum! Although most people dislike rhubarb for its tart taste, this dessert is anything but tart. Since the rhubarb is mixed with sugar before it is placed on the crust, it becomes sweet with only a slight hint of tartness, adding a nice undertone to the otherwise rich bar. I am sure that even the rhubarb-wary will enjoy this little treat! The shortbread crust is crisp and buttery and the sweet vanilla filling creamy smooth and melt-in-your-mouth good.  All of these aspects make these bars delicious and extremely addicting, so be prepared to go for seconds!

Note: These bars are best eaten the day they are made as the brown sugar crust softens on the second day. But even on the next day these bars remain extremely delicious! Serve them as they are or with a generous dollop of homemade whip cream, and enjoy the fruitful rhubarb season!

Vanilla Rhubarb Custard Bars
Adapted from Land O’Lakes
Yield: 12 servings

1/2 cup butter
1 cup GF Flour Mix*
1 teaspoon xanthan gum
1/3 cup sugar

2 cups sliced rhubarb
2/3 cup sugar, divided
2 eggs
1/4 cup GF Flour Mix*
3/4 teaspoon baking powder
1 teaspoon vanilla
1/4 cup firmly packed brown sugar

Heat oven to 350 F. Grease an 8-inch square baking pan.

Melt butter in a medium saucepan over medium-low heat. Cook, stirring constantly, until butter begins to turn golden brown (5-10 minutes). Immediately remove from heat. Add 1 cup GF flour mix, xanthan gum, and 1/3 cup sugar;  mix well (extra flour may need to be added in order to reach a dough-like/shortbread consistency). Press dough firmly into the bottom of the prepared pan.

In a separate bowl, combine sliced rhubarb and 2 tablespoons of sugar, mixing to coat all of the rhubarb. Set aside. Meanwhile, whisk together eggs and remaining sugar until mixture is fully incorporated. Add in 1/4 cup GF flour mix, baking powder, and vanilla until smooth.

Layer rhubarb on prepared crust and pour egg-mixture filling on top. Sprinkle 1/4 cup brown sugar evenly over the filling. Bake for 40 to 45 minutes or until top is golden brown and a toothpick inserted in center comes out clean. Cool at least 30 minutes before serving.

*GF Flour Mix
2 cups brown rice flour
2/3 cup potato starch
1/3 cup tapioca starch

16 thoughts on “Vanilla Rhubarb Custard Bars

  1. I made these yesterday … I put in 4 small eggs (48g each), added 1/2 cup of milk and nutmeg to the egg mix as I wanted something a bit more custardier and softer. Turned out really really well!! Very delicious!!!

    My brown sugar sort of sank in (probably because I added extra liquid), next time I’ll let it cook for a bit then sprinkle the brown sugar on top once it has set.

    The base was sooo yum, I thought I might have really burnt the butter, but it tasted fantastic. What a great idea to add more flavour!

  2. Made these bars with some fresh rhubarb from our CSA share and they were delicious! I followed the recipe as written and the crunchy brown sugar crust was sooooo good! will definitely make them again

    • Jo, thank you so much for letting me know how this recipe turned out for you! I’m so happy to hear that you enjoyed these bars. Nothing quite like a dessert with fresh rhubarb!

    • Hi Irene–great question! Xanthan gum is the binding agent commonly used in gluten-free baking. It helps provide the “glue” property that gluten supplies in wheat-containing baked goods. If you can’t find either xanthan gum or guar gum in the store (they can be used interchangeably), you might want to use an egg yolk instead, as this will supply some binding to prevent the crust from crumbling apart. Hope this helps!

      • What if I want to just use All-Purpose Flour? How much do I use? Then I would leave out the Xanthan gum for a recipe that would not be Gluten-Free?

      • Hi Phyllis,

        Since I’m gluten-free, I have not made this recipe with all-purpose flour. While I can’t advise on a tested method, I’d suggest trying the same amount of flour and simply leaving out the xanthan gum.

        Happy baking!

  3. Made these yesterday and they were very good. Had to add a lot of extra gf flour mix to get the dough right but it turned out well. Nobody suspected they were gluten free.

  4. Pingback: #weekendcooking @BethFishReads | Bay State Reader's Advisory

  5. Can you just use regular flour, and an egg yolk in the crust instead of the flour mix and xanthan gum? Have you made these bars this way instead?

    • Hi Karla,

      I have not tried this method personally since I’m gluten-free, but it’s worth a shot! If you’re using regular wheat flour, you likely don’t need the egg yolk because the gluten in the wheat will act as a binding agent. So in that case, I’d recommend just swapping out the flour and eliminating the xanthan gum.

      Happy baking!

  6. Made this today..used regular flour as didn’t need to be gluten free. It’s very good !! Will certainly make it again !

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