If you love fruity, jammy desserts with a buttery oat crumble, these Blueberry-Rhubarb Crumble Bars are going to be your new favorite treat. They’ve got that perfect balance of tart rhubarb and sweet blueberries, layered between a soft, chewy base and a golden, crunchy topping. Easy and perfect with a cup of coffee or a scoop of ice cream, these bars are delish!
These bars are simple to make and hold up beautifully, whether you’re serving them at a picnic, tucking them into lunchboxes, or just slicing one for an afternoon snack with coffee. Let them chill in the fridge, and they cut cleanly into neat, gorgeous bars.
And the best part? You can use frozen or fresh blueberries to make this homemade recipe. Grab your 8×8-inch (ish) baking dish and get baking!
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 and 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.
Add the rhubarb, blueberries, brown sugar, cornstarch, cinnamon, lemon juice, and lemon zest to a saucepan. Set it over medium-low heat and cover with a lid. Let the mixture cook down for about 15 minutes, stirring occasionally, until the rhubarb softens and the filling becomes thick and jammy. Remove from heat and let cool slightly.
While the filling is cooking, preheat your oven to 350°F. Line a square baking dish (an 8×8 or 9×9-inch pan works well) with parchment paper and lightly spray it with nonstick baking spray so nothing sticks.
In a large mixing bowl, stir together the flour, oats, brown sugar, baking powder, and salt. Add the cubed softened butter and use your clean hands or a pastry blender to work the butter into the dry mix until you get a crumbly texture. I love using this stainless steel pastry cutter; it’s sturdy, comfortable, and makes this step so much easier than using forks or fingers.
Set aside about ⅓ of the crumble mixture for the topping. Press the remaining ⅔ of the mixture evenly into the bottom of the lined pan. Use the bottom of a measuring cup or an offset spatula to firmly press it into the corners and smooth it out. Bake for 10 minutes.
Remove the base from the oven. Spread the warm blueberry-rhubarb filling over the crust, then sprinkle the remaining crumble mix over the top. Return to the oven and bake for 25–30 minutes until the top is golden and the filling is bubbling slightly around the edges.
Let the bars cool in the pan for 30 minutes at room temperature, then refrigerate for at least 2–3 hours to firm up. This helps the bars slice cleanly and hold their shape.
Chef Jenn’s Tips
- Use fresh rhubarb if it’s in season, but frozen works beautifully too; just don’t thaw it first.
- Chill the bars before slicing! Trust me, this is the key to neat, bakery-worthy squares.
- Add a dash of cardamom or ginger to the filling if you want to spice it up a bit.
- Want extra crunch? Toss a few chopped walnuts or pecans into the crumble topping.
Recommended
Make It A Meal
Serve these crumble bars with a scoop of vanilla ice cream or a dollop of whipped cream for dessert, or pair with a hot mug of coffee for a cozy breakfast treat. They’re also perfect picnic fare or bake-sale stars.
Storage
Store the bars in an airtight container in the refrigerator for up to 5 days. They also freeze beautifully, wrap individual bars in plastic wrap, and store in a freezer bag for up to 2 months. Let them thaw in the fridge overnight 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
- 1 teaspoon cinnamon
For The Crumble:
- 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 the rhubarb, blueberries, brown sugar, cornstarch, cinnamon, lemon juice, and zest in a saucepan. Cook over medium-low heat for about 15 minutes until thick and jammy. Let cool slightly.
- Preheat the oven to 350°F and line a square baking pan with parchment paper.
- In a large bowl, stir together the oats, flour, brown sugar, baking powder, and salt.
- Add the cubed butter and mix with clean fingers or a pastry cutter until crumbly. Set 1 ½ cups of the crumble aside for the topping.
- Press the remaining mixture into the prepared pan with an offset spatula and bake for 10 minutes.
- Spread the filling over the base, then top with the reserved crumble.
- Bake for 25–30 minutes, or until golden brown and bubbling.
- Cool completely, then refrigerate for 2–3 hours before slicing.
Notes
Chef Jenn’s Tips
- Use fresh rhubarb if it’s in season, but frozen works beautifully too; just don’t thaw it first.
- Chill the bars before slicing! Trust me, this is the key to neat, bakery-worthy squares.
- Add a dash of cardamom or ginger to the filling if you want to spice it up a bit.
- Want extra crunch? Toss a few chopped walnuts or pecans into the crumble topping.
