Blueberry Raspberry Oat Crumble Bars
These Blueberry Raspberry Oat Crumble Bars are the perfect combination of buttery oat crumble, sweet-tart berries, and a soft, jammy fruit center. They’re simple enough for a weekday treat but beautiful enough to serve at brunch, afternoon tea, or a family gathering.
The bottom crust is made from a golden oat mixture that becomes tender and slightly crisp around the edges. A thick layer of blueberry and raspberry filling goes in the middle, followed by more buttery crumble on top. As the bars bake, the berries become rich and jammy while the oat topping turns beautifully golden and crunchy.
They’re delicious warm, but they become even easier to slice once completely cooled.
Ingredients
For the oat crumble
- 1½ cups old-fashioned rolled oats
- 1½ cups all-purpose flour
- ¾ cup packed light brown sugar
- ½ cup granulated sugar
- ½ teaspoon baking powder
- ½ teaspoon salt
- 1 teaspoon ground cinnamon
- ¾ cup unsalted butter, melted
- 1 teaspoon vanilla extract
For the berry filling
- 1½ cups fresh or frozen blueberries
- 1½ cups fresh or frozen raspberries
- ½ cup granulated sugar
- 2 tablespoons cornstarch
- 1 tablespoon fresh lemon juice
- 1 teaspoon lemon zest
- 1 teaspoon vanilla extract
- Pinch of salt
Optional finishing
- Powdered sugar, for dusting
- Fresh blueberries and raspberries
- A little extra rolled oats
- Vanilla ice cream or whipped cream for serving
Instructions
1. Prepare the baking pan
Preheat your oven to 350°F (175°C).
Line an 8×8-inch or 9×9-inch baking pan with parchment paper, leaving some parchment hanging over the sides. This makes it much easier to lift the finished bars from the pan.
Lightly grease the parchment and the exposed sides of the pan.
2. Make the crumble mixture
In a large mixing bowl, combine the rolled oats, flour, brown sugar, granulated sugar, baking powder, salt, and cinnamon.
Stir everything together until evenly distributed.
Pour in the melted butter and vanilla extract. Mix with a fork or spatula until the ingredients are thoroughly combined. The mixture should look crumbly but hold together when pressed between your fingers.
Set aside about 1 cup of the crumble mixture for the topping.
3. Make the berry filling
Place the blueberries and raspberries in a medium saucepan.
Add the granulated sugar, cornstarch, lemon juice, lemon zest, vanilla extract, and a small pinch of salt.
Stir gently so the berries become coated.
Place the saucepan over medium heat and cook for approximately 5–8 minutes, stirring occasionally. The berries will begin releasing their juices and the mixture will gradually become thick and glossy.
If using frozen berries, you may need an additional couple of minutes.
You don’t want to completely break down all of the berries. A few whole or partially whole berries will give the finished bars a wonderful texture.
Once thickened, remove the filling from the heat and allow it to cool for a few minutes.
4. Form the bottom crust
Take the larger portion of the oat crumble mixture and press it firmly into the bottom of the prepared pan.
Use the back of a measuring cup or the bottom of a glass to create an even layer.
Pressing the crust firmly is important because it gives the bars a sturdy base that won’t fall apart when sliced.
Bake the crust for 10–12 minutes, just until it begins to look lightly golden around the edges.
Remove the pan from the oven.
5. Add the berry layer
Carefully spoon the warm berry mixture over the partially baked oat crust.
Spread it gently with a spatula so the berries cover the entire surface.
Try not to press too hard, as you don’t want to disturb the crust underneath.
The berry layer should be thick, glossy, and evenly distributed.
6. Add the crumble topping
Take the reserved crumble mixture and sprinkle it evenly over the berry filling.
You can leave some larger pieces of crumble intact. These create those delicious golden, crunchy pieces visible on top of the bars.
For an extra oat-filled texture, sprinkle a tablespoon or two of additional rolled oats over the top.
7. Bake
Return the pan to the oven and bake for approximately 30–38 minutes.
The bars are ready when the crumble topping is golden brown and the berry filling is bubbling around the edges.
Don’t worry if the center still looks slightly soft. The filling will continue to set as the bars cool.
If the top begins browning too quickly, loosely cover the pan with aluminum foil during the final few minutes of