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3 berry crumble bars made with oatmeal and brown sugar stacked on a white plate.

Mixed Berry Crumble Bars

Buttery oatmeal crumbles and sweet, juicy berries make these Mixed Berry Crumble Bars impossible to resist. These bars use the same mixture for the oatmeal base and crumble topping, then the middle is a juicy layer of strawberries, blueberries, raspberries & blackberries that tastes just like summer. 
Course Dessert
Cuisine American
Keyword Berry Crumble Bars
Prep Time 15 minutes
Cook Time 50 minutes
Total Time 1 hour 5 minutes
Servings 15 bars


Oatmeal Base & Topping

  • 2 ½ cups all-purpose flour
  • 1 teaspoon cinnamon
  • 1 ½ cups large flake or old-fashioned oats*
  • 1 cup white sugar
  • ½ cup brown sugar
  • 1 cup butter melted
  • 1 large egg

Berry Layer

  • 4 ½ cups mixed berries**
  • ½ cup white sugar
  • 2 tablespoons lemon juice*** freshly squeezed
  • 3 tablespoons cornstarch


  • Preheat the oven to 350F degrees.
  • Line a 9x13 inch pan with parchment paper leaving an overhang around all the edges, or line with aluminum foil & lightly grease.
  • In a large bowl stir together the flour, cinnamon, oats, & sugars
  • Stir in the melted butter and egg. It should look like wet sand.
  • Reserve about 1 ½ cups of the mixture for the topping. Then press the rest (about ⅔ of the batter) into the bottom of the prepared pan.
  • In a large bowl toss together the berries, sugar, lemon juice & cornstarch so that the berries are evenly covered.
  • Spoon the berry mixture over top of the base.
  • Crumble the remaining oatmeal mixture over top squeezing it in your palms so that large crumbles form.
  • Bake in the preheated oven for 45-50 minutes, or until the top is golden brown and you can see the berry mixture bubbling through.
  • Cool the pan on a wire rack at room temperature for 30 minutes, then move to the fridge to continue cooling (this can take up to 4 hours). before
  • Once the pan is completely cooled, slice into bars. Store in an airtight container in the fridge for up to 4 days.


*Do not use instant or quick oats - they behave more like flour and your bars won't turn out.
**I used a combo of strawberries, raspberries, blueberries & blackberries. Slice the strawberries and cut the large blackberries in half. If using frozen berries, do not thaw.
***If using frozen berries, only use 1 tablespoon lemon juice. Lemon juice could be substituted for water, but I find the flavor much better with lemon juice.