Blueberry-Rhubarb Crumble Bars
These Blueberry-Rhubarb Crumble Bars combine tart rhubarb with sweet blueberries in a soft base and a crisp oat topping. The filling turns jammy as it bakes, and the topping adds just the right crunch. They’re great with coffee or topped with ice cream.
They’re easy to prepare and hold their shape well once chilled. Perfect for picnics, packed lunches, or a quick afternoon snack.
Use either fresh or frozen blueberries; whatever you’ve got on hand. Just grab an 8×8-inch pan and start baking.
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Ingredients
For the Blueberry-Rhubarb Filling:
- Rhubarb – You can use fresh or frozen rhubarb.
- Blueberries – You can use fresh or frozen blueberries.
- Brown sugar
- Cornstarch
- Lemon juice
- Lemon zest
- Cinnamon
For The Crumble:
- Old fashioned oats – Also called rolled oats. Do not use instant oats or the texture will be all wrong.
- All-purpose flour
- Brown sugar
- Baking powder
- Unsalted butter – That’s 1 ½ sticks of butter.
- Salt
How To Make Blueberry-Rhubarb Crumble Bars
Scroll down for the full recipe card with exact measurements and printable instructions.
Place the rhubarb, blueberries, brown sugar, cornstarch, cinnamon, lemon juice, and lemon zest in a saucepan. Cook over medium-low heat with the lid on, stirring now and then, for about 15 minutes. The mixture should thicken and the rhubarb should soften. Take it off the heat and set aside to cool slightly.
While the filling cooks, preheat your oven to 350°F. Line an 8×8 or 9×9-inch square pan with parchment paper and lightly coat it with nonstick baking spray.
In a large bowl, mix the flour, oats, brown sugar, baking powder, and salt. Add the softened, cubed butter and use your hands or a pastry blender to mix until the texture is crumbly.
Set aside one-third of the crumble for the topping. Press the remaining two-thirds into the bottom of the prepared pan. Use a measuring cup or offset spatula to press it in evenly. Bake for 10 minutes.
Take the crust out of the oven and spread the fruit filling evenly on top. Sprinkle the reserved crumble over the filling. Bake for another 25–30 minutes, or until the top is golden and the filling is bubbling around the edges.
Let the bars cool in the pan at room temperature for 30 minutes, then chill in the fridge for 2 to 3 hours before cutting.
Chef Jenn’s Tips
- Don’t thaw frozen rhubarb before using.
- Chill completely before cutting to get clean slices.
- Add cardamom or ginger to the filling if you want a little spice.
- For crunch, mix chopped nuts into the crumble topping.
Recommended
Make It A Meal
Enjoy with ice cream, whipped cream, or coffee. Great for brunch, dessert, or as a bake-sale treat.
Storage
Keep in an airtight container in the fridge for up to 5 days. Freeze individual bars (wrapped) for up to 2 months. Thaw in the fridge before serving.
Blueberry-Rhubarb Crumble Bars
Ingredients
For the Blueberry-Rhubarb Filling:
- 1 ½ cups rhubarb sliced
- 6 ounces blueberries
- ½ cup brown sugar packed
- 2 tablespoons cornstarch
- 2 tablespoons lemon juice
- 1 tablespoon lemon zest
For The Crumble:
- 1 teaspoon cinnamon
- 1 ¼ cups old fashioned oats
- 1 ⅔ cups all-purpose flour
- 1 cup brown sugar lightly packed
- 1/2 teaspoon baking powder
- ¾ cups unsalted butter softened
- 1/4 teaspoon salt
Instructions
- Combine rhubarb, blueberries, brown sugar, cornstarch, lemon juice, lemon zest, and cinnamon in a medium saucepan. Cook over medium-low heat, stirring occasionally, for about 15 minutes, or until thickened and jam-like. Set aside to cool slightly.
- Preheat the oven to 350°F and line an 8×8-inch baking pan with parchment paper, leaving a slight overhang for easy removal.
- Mix oats, flour, brown sugar, baking powder, and salt in a large bowl. Add the softened butter and use your hands or a pastry cutter to mix until the texture is crumbly. Set aside 1½ cups of this mixture for the topping.
- Press the rest of the crumble mixture firmly into the bottom of the lined pan using a spatula or your hands. Bake for 10 minutes to set.
- Spread the cooled fruit filling evenly over the baked crust. Sprinkle the reserved crumble mixture on top.
- Return the pan to the oven and bake for 25–30 minutes, or until the top is golden and the filling is bubbling around the edges.
- Let the bars cool to room temperature, then place them in the fridge for 2 to 3 hours to firm up before slicing into clean squares.
Notes
Chef Jenn’s Tips
- Don’t thaw frozen rhubarb before using.
- Chill completely before cutting to get clean slices.
- Add cardamom or ginger to the filling if you want a little spice.
- For crunch, mix chopped nuts into the crumble topping.
