Rhubarb Crumble Bars

Stack of rhubarb crumble bars on parchment paper showing layers of golden shortbread base, pink jammy rhubarb filling, and crumble topping

Print Recipe

No ratings yet

Jammy rhubarb filling tucked between a buttery shortbread base and crisp crumble top. Made in an 8x8 pan for 9–16 bars.

Prep Time20

Cook Time50

Chill Time1

Total Time1 10

Course: Dessert

Cuisine: American

Servings: servings

Ingredients

Shortbread Dough (base + crumble top)

3/4 cups unsalted butter cold and cubed
2 cups all-purpose flour
⅓ cup granulated sugar
¼ cup powdered sugar
½ tsp kosher salt
1 tsp vanilla extract

Rhubarb Filling

3½ cups fresh rhubarb chopped into ½-inch pieces
2/3 cup granulated sugar
1½ tbsp cornstarch
1 tbsp lemon juice
1 tsp lemon zest
Pinch of salt

US Customary - Metric

Instructions

Preheat your oven to 350°F. Line an 8x8 pan with parchment paper, leaving overhang on two sides so you can lift the bars out cleanly. Lightly butter the exposed sides.
Add the rhubarb and sugar to a medium saucepan over medium heat. Stir to combine and cook, stirring occasionally, until the rhubarb breaks down and the mixture is bubbling and jammy, about 12–15 minutes. The liquid should reduce significantly, you want it thick, not soupy.
3½ cups fresh rhubarb, 2/3 cup granulated sugar
In a small bowl, whisk the cornstarch with 1 tablespoon of cold water until smooth, then stir it into the hot rhubarb. Cook 1 more minute until it thickens and coats the back of a spoon. Remove from heat and stir in the lemon juice, lemon zest, and pinch of salt. Set aside to cool slightly.
1½ tbsp cornstarch, 1 tbsp lemon juice, 1 tsp lemon zest, Pinch of salt
In a large bowl, whisk together the flour, granulated sugar, powdered sugar, and salt. Add the cold cubed butter and vanilla extract. Using your fingers or a pastry cutter, work the butter into the flour until the mixture looks like coarse, shaggy crumbs with some pea-sized butter pieces still visible. Do not overwork it. Pinch a bit, it should hold together when squeezed.
3/4 cups unsalted butter, 2 cups all-purpose flour, ⅓ cup granulated sugar, ¼ cup powdered sugar, ½ tsp kosher salt, 1 tsp vanilla extract
Reserve about one-third of the dough (roughly 200g / 1½ cups) and refrigerate it. Press the remaining two-thirds firmly and evenly into the bottom of your prepared pan. Use the bottom of a measuring cup to get it smooth and flat, making sure it reaches into the corners.
Bake the crust for 15–17 minutes until it looks dry on top and just barely starting to turn golden at the edges. Remove from the oven.
Spread the rhubarb filling evenly over the warm par-baked crust, all the way to the edges. Take the reserved cold dough out of the fridge and crumble it over the top with your fingers, breaking it into irregular pieces of varying sizes. You want some gaps where the filling peeks through, don't pack it down.
Return the pan to the oven and bake for 28–32 minutes, until the crumble top is golden and the filling is bubbling at the edges. If the crumble is browning too fast, tent loosely with foil for the last 10 minutes.
Let the bars cool in the pan for at least 30 minutes at room temperature, then transfer to the fridge for 1 hour. This step is non-negotiable, the filling needs to fully set before you cut or you'll get a messy, soft slice. Lift out using the parchment overhang, slice into 9 large or 16 smaller bars, and serve.

Notes

Storage: Keep in an airtight container in the fridge for up to 5 days. They actually get better on day 2 once the filling firms up fully.
Rhubarb tartness: If your rhubarb is very tart, bump the filling sugar up to 3/4 cup. Taste it after it cooks down, it should be bright and tangy but not mouth-puckering.
Strawberry variation: Use 1/4 less rhubarb and stir in ½ cup (80g) of diced fresh strawberries in the last 2 minutes of cooking the filling for a classic combo.
Serving tip: Dust with powdered sugar right before serving for a clean finish.

Nutrition