Mixed Berry Crumble Bars Recipe

I tucked a secret layer into Berry Crumble Bars using only oats and fresh berries, and even I was surprised by the twist.

I cant stop thinking about these Mixed Berry Crumble Bars from Just SO Tasty. Flaky oat streusel meets bright jammy pockets of mixed berries (strawberries blueberries raspberries), and somehow it’s more than the sum of its parts.

I used old fashioned rolled oats in the crumble so you get that toothsome bite that keeps pulling you back for another square. There’s a small, sneaky change during baking that makes the filling glisten differently, and I bet you’ll notice it too after the first taste.

If you hunt down Berry Crumble Bars or love Berry Dessert Recipes that scream summer, this one will make you curious.

Ingredients

• Rolled oats add chewy texture, hearty fiber for fullness, plus slow releasing carbohydrates.
• Light brown sugar gives caramel warmth and sweetness but adds extra simple sugars.
• Melted butter brings richness and helps bind crumbs, adds saturated fat and deep flavor.
• Vanilla lifts aroma and flavor, makes the bars smell cozy and homey.
• Berries are tart and sweet, packed with vitamin C fiber and antioxidants.
• Cornstarch thickens berry filling so it sets, it’s pure starch with almost no nutrition.
• Lemon juice brightens flavor, adds acid to balance sweetness and cut gluey taste.
• Flour gives structure and chew, mainly carbs so low in protein.

Ingredient Quantities

• 1 1/2 cups all purpose flour
• 1 1/2 cups old fashioned rolled oats
• 1 cup packed light brown sugar
• 1/2 teaspoon baking powder
• 1/2 teaspoon salt
• 12 tablespoons unsalted butter melted
• 1 teaspoon vanilla extract
• 4 cups mixed berries (strawberries blueberries raspberries)
• 1/2 cup granulated sugar
• 3 tablespoons cornstarch
• 1 tablespoon lemon juice
• pinch of salt

How to Make this

1. Preheat oven to 350 F (175 C). Line a 9×13 inch pan with parchment leaving an overhang, or grease it well.

2. In a large bowl stir together 1 1/2 cups flour, 1 1/2 cups rolled oats, 1 cup packed light brown sugar, 1/2 teaspoon baking powder and 1/2 teaspoon salt.

3. Pour in 12 tablespoons melted unsalted butter and 1 teaspoon vanilla, mix with a fork or your hands until coarse clumps form. Reserve about half of this mixture for the topping and press the other half firmly into the prepared pan to form the crust.

4. Bake the crust 12 to 15 minutes until set and just starting to brown. Remove from oven and let cool slightly while you make the filling.

5. In a medium bowl toss 4 cups mixed berries with 1/2 cup granulated sugar, 3 tablespoons cornstarch, 1 tablespoon lemon juice and a pinch of salt. Let sit 5 minutes to macerate, then transfer to a small saucepan and cook over medium heat 2 to 4 minutes until the mixture is glossy and slightly thickened; cool 5 minutes. (If you prefer you can skip the stovetop step but cooking helps prevent a soggy bar.)

6. Spread the berry filling evenly over the par-baked crust.

7. Crumble the reserved oat mixture over the berries, scatter it so some fruit still shows and press very lightly so crumbs stick but dont compress the topping flat.

8. Bake 25 to 30 minutes until the top is golden and the filling is bubbling at the edges.

9. Cool completely in the pan on a wire rack, at least 1 to 2 hours so the filling sets. Use the parchment overhang to lift the slab from the pan, slice into bars, serve room temp or chilled with ice cream.

Tip: If using frozen berries, thaw and drain excess liquid or add an extra tablespoon of cornstarch. Press the crust firmly and chill briefly before baking if your butter was very warm, it makes a nicer, less crumbly base.

Equipment Needed

1. 9×13 inch baking pan, lined with parchment leaving an overhang or greased well
2. Parchment paper (and scissors to trim if you want)
3. Mixing bowls — one large plus one medium
4. Measuring cups and measuring spoons
5. Fork (or your hands) and a silicone spatula for mixing and spreading
6. Small saucepan for cooking the berries
7. Wire cooling rack
8. Oven (set to 350 F) and oven mitts
9. Fine mesh sieve or colander for draining thawed frozen berries (optional)

FAQ

Mixed Berry Crumble Bars Recipe Substitutions and Variations

• All purpose flour: Swap with whole wheat pastry flour 1:1 for a nuttier, slightly denser bar. Or use a gluten free 1:1 baking blend 1:1 if you need GF. If you want to try almond flour, use about 3/4 cup almond flour per 1 cup AP and add a binder (egg or a tablespoon of flax+water), the bars will be more tender and a bit oily.
• Old fashioned rolled oats: Use quick oats 1:1 for a finer, more compact crumble, it’ll bind better. Or replace with 1 cup chopped nuts (almonds, pecans, walnuts) for crunch and lower carbs. Toast the nuts first for extra flavor.
• Unsalted butter melted: Coconut oil works great 1:1 for dairy free, or use vegan stick butter 1:1. For a lower fat option you can try applesauce or mashed banana about 3/4 cup per 1 cup butter, but expect a softer, less flaky texture.
• Cornstarch: Swap with arrowroot powder 1:1 or tapioca starch 1:1 to thicken the berry filling. If you only have flour use about 2 tablespoons flour for every 1 tablespoon cornstarch, though the filling will be less glossy and slightly thicker in flavor.

Pro Tips

1) Press the crust really firm, then chill it for 10-15 minutes if your butter felt warm, it helps the base hold together instead of turning into crumbs when you slice. If you still get a loose crust, give it an extra minute or two in the oven until the edges just start to brown.

2) If you use frozen berries, thaw and drain them well, then add an extra tablespoon of cornstarch (or 1 Tbsp instant tapioca) and a splash more lemon, toss and cook the filling briefly so its glossy and not soupy. Dont skip this step or the bars will be soggy.

3) To prevent the filling from seeping into the crust, sprinkle a thin layer of quick oats or 1 tablespoon of dry cornstarch over the par-baked crust before you add the fruit, that little barrier soaks up stray juice without changing the flavor.

4) Cool completely before slicing, like at least 1-2 hours in the pan, and even chill for cleaner cuts if you want neat bars. They also freeze great, individually wrapped, so slice first if you want grab-and-go treats later.