The Best Blueberry Crumb Bars

These Blueberry Crumb Bars are the kind of old-fashioned fruit dessert I keep coming back to: a buttery, tender crumb crust, a thick layer of juicy blueberries, and a golden crumble topping that gives every bite a little texture. The berries turn wonderfully jammy in the oven, while a touch of cinnamon adds warmth without overpowering their fresh, sweet-tart flavor.

This is a true keeper because the same simple crumb mixture does double duty as both the crust and topping. There is no rolling dough, no mixer required, and fresh blueberries need very little preparation. I especially like these for family gatherings because they slice neatly once cooled, and the kids tend to make them disappear faster than I expect.

They are equally good as an afternoon treat, lunchbox dessert, or casual summer dessert with a scoop of vanilla ice cream. You can also swap in other berries when blueberries are not at their best.

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Ingredients

Crust and Crumb Topping

3 cups all-purpose flour

1 cup granulated sugar

1 tsp baking powder

¼ tsp salt (Optional)

⅛ tsp ground cinnamon (Optional)

1 cup unsalted butter, cold and cut into small cubes

1 large egg

Blueberry Filling

4 cups fresh blueberries

½ cup granulated sugar

1 tbsp cornstarch

Instructions

1. Preheat the oven to 190°C / 375°F. Lightly grease a 9-by-13-inch baking pan.
2. In a large bowl, whisk together the flour, 1 cup sugar, baking powder, salt, and cinnamon.
3. Add the cold butter and egg. Cut them into the flour mixture with a pastry cutter or fork until coarse, moist crumbs form. The mixture should remain crumbly rather than becoming a smooth dough.
4. Press about half of the crumb mixture firmly and evenly into the bottom of the prepared pan.
5. In another bowl, combine the remaining ½ cup sugar with the cornstarch. Add the blueberries and toss gently until evenly coated.
6. Spread the blueberry mixture over the crust, including any sugar mixture remaining in the bowl.
7. Sprinkle the remaining crumb mixture evenly over the blueberries. Leave some larger crumbs for extra texture.
8. Bake at 190°C / 375°F for about 45 minutes, or until the top is lightly golden and the blueberry filling is bubbling around the edges.
9. Cool completely in the pan before cutting into 15 bars. Cooling allows the berry filling to set so the bars hold their shape.

Cooking Notes

Keep the butter cold until you mix the dough. Cold butter creates a more tender, crumbly texture, while softened or melted butter can make the crust dense.

Do not crush the blueberries while mixing them with the sugar and cornstarch. Whole berries release their juices gradually as they bake.

The bars may look slightly loose while hot. Let them cool completely before slicing; the cornstarch-thickened filling continues to set as it cools.

Fresh raspberries, blackberries, chopped strawberries, or a combination of berries can replace the blueberries. Very juicy berries may require an additional 1 to 2 tsp cornstarch.

If using salted butter, omit the optional salt.

Nutrition

The raw ingredients weigh roughly 55 oz before baking. Moisture loss during baking brings the finished batch to approximately 49 to 51 oz, making each of the 15 bars about 3.3 oz.

Yields: 15 servings

Recommended Serving Size: 1 bar, approximately 3.3 oz

Estimated Nutrition per Serving

Calories: 318 kcal

Fat: 14.0 g

Carb: 45.0 g

Protein: 3.0 g

Recipe Science

These bars combine a flour-and-butter crumb mixture with a blueberry filling thickened by cornstarch. The same dough functions as both the pressed bottom crust and the loose topping, which simplifies preparation while producing two distinctly different textures. Blueberries supply moisture and acidity, while sugar balances their tartness and encourages the filling to become syrupy during baking.

Cold butter coats portions of the flour rather than blending completely into it. As the butter melts in the oven, it contributes richness and helps create a tender, crumbly structure. Cornstarch absorbs some of the liquid released by the blueberries and thickens it as the filling heats. Approximately 45 minutes at 190°C / 375°F gives the crust time to brown while allowing the fruit juices to bubble and thicken.

The bars store well in an airtight container for about two days at room temperature or several days refrigerated. Chilling creates firmer slices; bringing them back toward room temperature restores a softer crumb. Other berries can be substituted, although especially juicy fruit may require slightly more cornstarch.

Dietary Notes & Health Alerts: Estimated sodium is about 77 mg per serving, well below 20% of the FDA Daily Value of 2,300 mg. Saturated fat is approximately 4 g, which equals 20% of the 20 g Daily Value. Added sugar is approximately 20 g per bar, or about 40% of the 50 g Daily Value, which is considered high. For a lower-added-sugar version, the sugar in the blueberry filling can be reduced modestly; however, reducing the sugar in the crumb mixture too aggressively can affect browning and texture.

Why You’ll Love This Recipe

• One Dough, Two Layers: The same buttery crumb mixture forms both the crust and topping, making preparation especially simple.
• Juicy Berry Center: Blueberries bake into a thick, jammy filling without requiring a separate cooked sauce.
• No Mixer Needed: A bowl, fork or pastry cutter, and baking pan are all you need.
• Family-Friendly: The familiar combination of buttery crumble and sweet berries makes these easy to serve to both kids and adults.
• Easy to Customize: Blueberries can be replaced with raspberries, blackberries, strawberries, or mixed berries.

FAQ

• Can I use frozen blueberries?: Yes. Use them straight from frozen rather than thawing them first, and expect the bars to need a few additional minutes in the oven.
• Why did my blueberry filling turn runny?: The bars were probably sliced while still warm. Cornstarch-thickened berry filling becomes substantially firmer as it cools.
• Can I make these bars ahead of time?: Yes. Bake them a day in advance, cool completely, cover, and refrigerate. They often slice even more cleanly the next day.
• Can I use shortening instead of butter?: Yes. Shortening produces a slightly more tender, less buttery crumb. Butter provides noticeably more flavor.
• How do I know when the bars are done?: Look for a lightly golden topping and blueberry juices bubbling around the edges of the pan.

Conclusion

These Blueberry Crumb Bars are one of those wonderfully practical desserts that proves simple ingredients can make something worth saving. Cooking is always a little personal, so feel free to change the berries, adjust the cinnamon, or serve these exactly the way your family likes them.

What berry combination would you try in your next batch?

Happy baking, and enjoy every bite!