Rhubarb Crumb Bars

After my last rhubarb cake post, I was so taken with the flavor of rhubarb that I haven’t been able to get it out of my head. Big piles of the ruby red stalks piled high at the farmers market weren’t helping me get my mind off it either. We happened to have a big gathering at our house, which gave me the perfect excuse to adapt a recipe I’ve always thought would taste delicious with rhubarb, and boy was I ever right.

I tried swapping out rhubarb for blueberries in this great recipe from smitten kitchen. This recipe has been a stand by in my kitchen from the very first time I made it. This recipe is somewhere between a crumble and a cookie. It’s got a great shortbread type crust that’s just the right amount of dry, a rich gooey layer of fruit, and, the most important part, a thick layer of crusty, crumbly topping that’s so delicious I found myself sneaking bits and pieces off the top until my guests arrived. 

But the great end result is not to say that testing out a new recipe was easy and didn’t take some tinkering and a leap of faith. That’s part of what we’re trying to do here at soysugarsherry, push ourselves to try new things and demonstrate to our readers that it’s not the plunge it seems to be. So I thought I’d share my failure because I learn every bit as much from trying and falling flat on my face.

Swapping in the different fruit was easy, it worked on the first try. But unable to leave well enough alone, I made the recipe again but thought I’d try to both reduce the recipe size so it could be baked in a more common pan size and try to adjust the crumb topping with a technique I’ve used before with great results where you mix melted butter in to the dry ingredients. Turns out the first lesson was that you should never try to test too many variables at once. There’s a reason why I never became a scientist. Moving in measured, rational, slow steps has never been my strong suit. I like to tell myself there’s some creativity that shooting from the hip brings. Hold on to that thought and apply it to grain salads or marinades but not to baking where ratios and chemistry are the name of the game.

My second lesson was some recipes aren’t easy to scale for different pan sizes, especially those with a single egg. My adjustments resulted in a bar cookie with too thick a base layer and too much dry, crumbly topping. Turns out too much of a good thing can be a bad thing. By increasing the amount of dry ingredients, I had thrown off the ratio of dry to fruit filling which translated into a dry, crumbly bar cookie with an unpleasing appearance and texture. My last lesson was that while I’ve had great results for crumb cakes stirring melted butter into dry ingredients to create a congealed crumb topping, in this instance using cold butter was better. The cold butter meant that the crumb remained looser and therefor was more easily incorporated into the fruit layer resulting in a lovely golden topping melting into pockets of roasted fruit. All this is not to say don’t experiment. I’m hopeful that I now better understand the strengths of this recipe and can unequivocally recommend it to you, knowing the how and why of what makes it work.

Tips and Tricks:

  • You’ll read over and over again when incorporating cold butter into a recipe to mix until it resembles “coarse sand” or has “mostly been incorporated” or pieces are “the size of small peas.” And I never really knew what that meant. But now after years and years of mushing butter into flour with my hands, I can safely say that something like the above picture is what you’re shooting for. There are some slightly larger clumps about 1/2 and inch and smaller and some dry crumbs, but once you add the liquid portion of the recipe, these pieces will come together into a cohesive dough.
  • There are a couple of tricks to help get these bars out of the pan easier.  First grease the pan evenly. I like to start by rubbing the pan with the butter wrappers from the sticks of butter I use for the recipe, then cut at least 1 tablespoon of butter and let it sit out while I prep the rest of the recipe. Then using the butter wrapper or a paper towel, fully grease the pan again. It also helps to fully cool these bars and even refrigerate them, given their high butter content, before trying to cut them. I used a small angled spatula to get out the first couple bars and then it got easier. You can also line the pan with a big sheet of parchment that comes up the sides, which will allow you to pull the whole slab out but only attempt this if you’ve refrigerated the bars so they don’t cave in.
  • I always cut rhubarb on a plastic cutting board and immediately rinse it. Rhubarb’s bright red color is not nearly as enticing once it’s a permanent stain on your wood cutting board.
  • The corn starch is added to the recipe to help as a thickener for the fruit juices. This is a great trick for making pies, crumbles or other fruit desserts. Flour can also be used as a stand-in for the same trick. While it’s not absolutely necessary in this recipe, since rhubarb isn’t as juicy, I left in the cornstarch in case you sub out other, juicier fruit like berries. Feel free to adjust the amount of corn starch based on the type of fruit and how much it leaks; strawberries or raspberries for example might call for more than blueberries.

Rhubarb Crumb Bars

A great, basic recipe for crumb bars that can be adapted to highlight any fresh, in-season produce you happen to have on hand. While you can change out the fruit, the rest of the recipe is not so easily adapted as this is just the right balance of dry crumb to dense buttery flavor and texture. It serves as the perfect base for highlighting the fruit. I could see, however mixing in half granulated sugar and half brown sugar or turbinado sugar for a deeper, caramel flavor. I could also see substituting orange for lemon in this recipe.

Quantity: roughly 36 one-inch bars in a 10 x 13″ pan

Time to Prepare: 1 hour and 15 minutes

1 cup white sugar
1 teaspoon baking powder
3 cups all-purpose flour
1 cup cold unsalted butter (2 sticks or 8 ounces)
1 egg, beaten
1/4 teaspoon salt
Zest of one lemon, juice from half a lemon
4 cups rhubarb thinly sliced into 1/4″ or smaller rounds
1/2 cup white sugar
1 tablespoon cornstarch

1. Preheat the oven to 375 degrees. Grease a 9×13 inch pan.

2. In a medium bowl, stir together the flour,  baking powder, and salt. In another smaller bowl put the sugar, then mix in the lemon zest and rub it into the sugar between your fingers to incorporate the zest throughout 1 cup of the sugar. Add this to the flour mixture, stirring with a fork.

2. Cut the cold butter into 1/2″ pieces then add to the dry ingredients. Using your fingers, pinch and work the butter into the dry ingredients until it’s broken down into pieces about the size of peas (see above in post for photo of what this looks like). The mix will be dry and very crumbly but come together when pressed. Next blend in the beaten egg, using the fork. Pat half of dough into the prepared pan, pushing down with your fingertips to evenly cover the base of the pan.

3. In another bowl, stir together the 1/2 cup sugar and cornstarch. Gently mix in the sliced rhubarb and squeeze the lemon juice on top of it. Then sprinkle the mixture evenly over the crust. Crumble remaining dough over the rhubarb layer. Do this by grabbing handfuls of dough and squeezing them in your palm to form clusters of dough. Drop these all over the top layer. They will fall apart but that’s okay. You want clusters roughly of an inch or so in size sprinkled all over the top in a thick layer. Take the remaining dry bits and pieces of dough and small crumbs and evenly distribute over the top, don’t worry – they’ll back into a delicious top crust.

4. Bake in preheated oven for 45 minutes, or until top is slightly brown. Cool and cut into small squares so you can eat more of these in a sitting.

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