Buttery oat crumble bars layered with a sweet-tart mixed berry filling and baked until golden—an easy, crowd-pleasing treat perfect for dessert or snacking.
Preheat oven to 350°F. Line an 8x8" baking dish with parchment paper.
In a large bowl, combine oats, flour, salt, baking powder, and brown sugar. Stir in melted butter until crumbly.
Press 2/3 of the mixture into the prepared pan. Bake on center rack of preheated oven for 10 minutes.
While the crust is baking, in another bowl, mix raspberries, blackberries, and brown sugar. Lightly mash. Stir in cornstarch, lemon juice, vanilla, lemon zest, and strawberry preserves.
Spread berry mixture over crust. Top with remaining crumble.
Bake an additional 35–40 minutes, until golden.
Allow bars to cool 40–50 minutes before slicing.
Notes
Calories are automatically generated. For best results calculate based on your exact ingredients.Recipe Notes:
Use the bottom of a measuring cup to press the crust evenly.
Make sure the cornstarch is fully mixed into the berries to help thicken the filling.
Add a little extra cornstarch if your berries are especially juicy.