Blueberry Crumb Bars

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I first made these blueberry crumb bars on a humid summer afternoon when the market had piles of ripe berries and I needed something that felt like a dessert and a snack at once. They’re a buttery oat-crust sandwich with a bright, lightly thickened blueberry filling — easy to pull together and impressive on the picnic blanket, brunch table, or packed in a lunchbox. If you like lemon-scented berries and a crisp-tender crumble, this is the kind of recipe you’ll return to all season. For a citrus-forward cousin, I sometimes compare them to my lemon crumb bars when serving guests who love a tangy finish.

Why you’ll love this dish

These bars balance sweet, tart, and buttery textures without fuss. The crumb base is part shortbread, part oat cookie — sturdy enough to hold juicy berries but tender enough to break apart with a fork. They’re great for:

• Casual gatherings and potlucks (make ahead and transport well).
• Kid-friendly snacks that aren’t overly sweet.
• Using up a basket of fresh blueberries in one pan.

"The blueberries stay vibrant and the crumb top stays crunchy — perfect for brunch or afternoon tea."

Beyond convenience, there’s a real flavor win here: lemon juice brightens the fruit, and the cornstarch gives a glossy, set filling so you don’t get a soggy bottom.

How this recipe comes together

Before you dig into the bowls, here’s the quick process so you know what to expect:

1. Whip butter and sugar until light to create a tender crumb.
2. Stir in dry ingredients and oats to form a sandy dough.
3. Press half the dough into the pan for a firm base.
4. Toss berries with lemon and cornstarch to thicken and spread over the crust.
5. Crumble the remaining dough on top and bake until golden.
6. Cool fully so the filling sets before slicing into bars.

This sets expectations: active time is mostly mixing and assembly, bake time is 30–35 minutes, and cooling is essential.

What you’ll need

• 1 cup unsalted butter, softened (can substitute 3/4 cup salted butter and omit added salt)
• 1 cup granulated sugar (or 3/4 cup coconut sugar for a deeper caramel note)
• 2 cups all-purpose flour (swap 1:1 gluten-free flour blend for GF)
• 1/2 teaspoon salt
• 1/2 teaspoon baking powder
• 1 cup rolled oats (old-fashioned; use certified gluten-free oats if needed)
• 2 cups fresh blueberries (frozen work — see tips)
• 1 tablespoon lemon juice
• 1 tablespoon cornstarch (arrowroot can be used for a corn-free option)

If you want a nuttier crust, stir in 1/2 cup finely chopped almonds or walnuts with the oats. For a lighter crust texture, pulse the oats once in a blender to break them down slightly.

Step-by-step instructions

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1. Preheat the oven to 350°F (175°C). Grease a 9×9-inch baking pan or line it with parchment, leaving an overhang for easy removal.
2. In a large bowl, cream the softened butter and sugar with a wooden spoon or electric mixer until pale and fluffy, about 2–3 minutes.
3. In a separate bowl, whisk together the flour, salt, and baking powder. Gradually add the dry mix to the butter-sugar until combined.
4. Fold in the rolled oats until the mixture looks sandy and holds together when pressed.
5. Reserve about half the mixture for the topping. Press the other half firmly and evenly into the bottom of the prepared pan to form the crust. Use the bottom of a measuring cup to compact it.
6. In another bowl, toss the blueberries with lemon juice and cornstarch until evenly coated. Spread this fruit mixture in an even layer over the crust. (If using frozen berries, do not thaw completely — see tips.)
7. Crumble the remaining oat mixture over the blueberries. It’s okay if there are large and small crumbs; the texture is lovely that way.
8. Bake for 30–35 minutes, until the top is golden and the filling bubbles at the edges. Rotate the pan halfway through baking for even color.
9. Remove from the oven and cool completely on a wire rack. Chill 30–60 minutes if you want cleaner slices, then lift from the pan and cut into bars.

For a cleaner presentation, chill before slicing and wipe your knife between cuts.

Best ways to enjoy it

These bars are versatile. Try serving them:

• Warm with a scoop of vanilla ice cream for a rustic dessert.
• At room temperature on a brunch board alongside coffee and fresh fruit.
• Chilled from the fridge as a grab-and-go snack with a dollop of Greek yogurt.

For a pretty plate, dust lightly with powdered sugar and garnish with a few whole berries and a lemon twist.

Storage and reheating tips

Short-term: Store cooled bars in an airtight container at room temperature for up to 2 days. For longer freshness, refrigerate up to 5 days.
Freezing: Wrap bars individually or freeze the whole pan (tightly covered) for up to 3 months. Thaw overnight in the fridge.
Reheating: Warm bars in a 300°F oven for 5–8 minutes or microwave a single bar for 15–20 seconds to refresh the crumb.
Food safety: Because these contain fresh fruit, keep leftovers refrigerated if your kitchen is warm and consume within five days.

Pro chef tips

• Don’t overmix the dough once flour is added; you want a tender crumb, not a dense bar.
• Press the bottom crust firmly — a compact base prevents the filling from leaking through.
• If using frozen blueberries, toss them in cornstarch and add them frozen; thawed berries can bleed too much, making the filling runny. For more ideas on working with berries, I often reference other fruit-crumble techniques like these easy cranberry crumble bars.
• To prevent a soggy bottom, chill the assembled pan for 10–15 minutes before baking to firm the crust slightly.

Creative twists

• Lemon-Blueberry Streusel: Mix 1/4 cup brown sugar and 1/4 cup cold butter into the topping for a streusel finish.
• Mixed Berry: Swap half the blueberries for raspberries or blackberries for complex flavor. (See a raspberry take here: raspberry crumble bars.)
• Vegan version: Use coconut oil or a vegan butter substitute and a flax "egg" (1 tbsp ground flax + 3 tbsp water) to bind.
• Nutty crust: Replace 1/2 cup of the oats with finely chopped pecans or almond meal.
• Mini bars: Use a muffin tin to make individual-sized bars for packed lunches or parties.

Your questions answered

Q: Can I use frozen blueberries?
A: Yes. Use them frozen and toss directly with lemon and cornstarch. Frozen berries are juicier, so don’t thaw or they’ll release extra liquid.

Q: How long does it take to make these from start to finish?
A: Active hands-on time is about 20–25 minutes. Bake 30–35 minutes and allow 30–60 minutes cooling for best slicing — plan roughly 1.5 hours total.

Q: How do I know when they’re done?
A: The top should be golden-brown and the filling should bubble lightly at the edges. If the top is darkening too fast, tent with foil.

Q: Can I make these ahead for a gathering?
A: Yes — bake, cool, then refrigerate for up to 2 days or freeze for longer. Bring to room temperature or warm briefly before serving.

Q: Any substitutions for cornstarch?
A: Use arrowroot one-for-one, or for a less glossy but still thick filling, use 2 teaspoons tapioca starch.

Conclusion

If you want background inspiration or variations from other home cooks, the blueberry crumb bars – smitten kitchen post offers a lovely narrative and tweaks. For a slightly different crumble technique and topping ideas, check out Blueberry Bars with Crumble Topping – Cooking Classy. Allrecipes has a long-running community-tested take you can compare with this version at Blueberry Crumb Bars Recipe. For another blogger’s perspective and step photos, see Blueberry Crumb Bars — elisabeth & butter.