Mixed Berry Crumble Bars

Why You’ll Love This Recipe

I adore how these bars blend comforting oat crumble with bright berry flavors. The buttery, oatmeal-packed base and topping provide satisfying texture, while the juicy berry layer brings in natural sweetness and tang. They’re perfect made with fresh or frozen berries and ideal as an easy dessert, breakfast, or snack.

ingredients

(Here’s a tip: Check out the full list of ingredients and measurements in the recipe card below.)

• For the base & crumble topping:

  • 2½ cups all-purpose flour

  • 1½ cups old-fashioned oats

  • 1 cup granulated sugar

  • ½ cup brown sugar

  • 1 teaspoon ground cinnamon

  • 1 cup melted butter (preferably salted)

  • 1 large egg

• For the berry layer:

  • 4½ cups mixed berries (strawberries, raspberries, blueberries, blackberries), fresh or frozen

  • ½ cup granulated sugar

  • 2 tablespoons lemon juice (1 Tbsp if berries are frozen)

  • 3 tablespoons cornstarch (to thicken filling)

directions

1. Preheat oven to 350 °F (175 °C) and line a 9×13″ pan with parchment paper, leaving an overhang.

2. In a large bowl, whisk flour, oats, sugars, and cinnamon. Stir in melted butter and egg until mixture resembles wet sand.

3. Reserve about 1½ cups of the crumble mixture for topping, and press the remaining mixture evenly into the bottom of the pan.

4. In another bowl, toss berries with sugar, lemon juice, and cornstarch—straining excess juice if needed to avoid sogginess.

5. Spread berry mixture evenly over the crust. Crumble the reserved topping in clusters over the berries.

6. Bake 45–50 minutes, until topping is golden and berry filling is bubbling. Frozen berries may require an extra 10 minutes.

7. Cool bars at room temperature for about 30 minutes, then chill in the fridge for at least 3–4 hours—or longer—to allow clean slicing.

Servings and timing

• Yield: ~15 bars

• Prep time: ~15 minutes

• Cook time: ~45–50 minutes

• Cooling time: ~3–4 hours (plus an optional fridge chill)

• Total time: ~4 hours (mostly hands-off)

Variations

• Use any combination of berries—or add preserves or jam for a more intense flavor.

• Include almond flour and baking powder for a richer, slightly cakier base.

• Add spices like ginger or extra cinnamon to the base for extra warmth.

storage/reheating

I store slices in an airtight container in the fridge for up to 4 days. They freeze well too—just thaw in the fridge before enjoying. The crumble stays crisp and the filling maintains its jammy texture.

FAQs

Can I use frozen berries?

Yes—don’t thaw before use. Reduce lemon juice to 1 tablespoon and extend baking time to ensure the filling sets.

What kind of oats should I use?

Use old-fashioned rolled oats for the crumble texture. Avoid instant oats, which tend to make it too soft.

How do I prevent soggy bars?

Strain off excess juice from berries, and ensure the crust is pressed firmly. Also, chilling fully before slicing helps everything set nicely.

Can I make them gluten-free or vegan?

Yes—sub gluten-free flour and vegan butter. For a GF version, see adaptations in other recipe notes.

Can I add a glaze?

Definitely—brush on a simple powdered sugar glaze or grain-free maple drizzle just before serving to dress them up.

Conclusion

I love these Mixed Berry Crumble Bars for how they combine effortless prep with bold summer flavor. They’re perfect to bake ahead, share, or enjoy any time you crave that cozy fruit-and-oat combo. And with lots of flexibility for ingredient swaps, they’ve become a staple on my baking list—just grab and go or plate them with a scoop of ice cream for extra delight.