Blueberry Oat Crumble Bars give you all the flavor of a fresh blueberry pie (juicy filling included) without ever touching a rolling pin. One bowl of oats does double duty: press most of it into the pan as the base, then scatter the rest over the filling as the topping.
That's the trick. No crust to roll, and no need to give up your whole afternoon.
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Why This One Works
Most blueberry bar recipes overlook one crucial detail: cooling time matters just as much as bake time. Slice too early, and your filling runs all over the pan. To fix this, I give the blueberries a quick head start on the stovetop to thicken and concentrate the juices before they ever hit the oven. Paired with a full cool down, you get thick, jammy layers and clean, picture-perfect slices every single time.
These are the bars I bring when I want pie at a picnic but don't want to deal with the mess of cutting and serving individual slices. It's about an hour of active time, then about 2 ½ hours to cool before you cut in. These hold well covered in the fridge, so they're an easy make-ahead pick for a potluck.
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Ingredients and Substitutions
Ingredient notes
- Blueberries: It's hard to go wrong with fresh blueberries in the summer, but if you're craving blueberry pie bars out of season, frozen berries work just as well in this recipe.
- Old-fashioned oats: Opt for rolled oats (also called old-fashioned oats) for the best texture. Quick oats can be used in a pinch, but they will absorb more moisture and create a softer crumble. You can also swap some of the oats for chopped nuts or seeds in the crumble for a bit of crunch.
- Lemon juice and zest: Blueberries and lemon are a match made in heaven, but if you don't have a lemon handy, you can use a lime instead. It will give it a similar brightness and hint of citrus flavor as a lemon.
- Butter: For a vegan option, use melted vegan butter or coconut oil.
How to Make Blueberry Oat Crumble Bars
- Make the crust: Combine flour, oats, sugars, cinnamon and baking powder in a large bowl. Stir in melted butter and vanilla.
- Bake: Reserve ⅓ of the oat mixture and press the remaining into an 8" pan lined with parchment paper. Bake for 10 minutes.
- Berry filling: Stir together the blueberries, lemon juice and zest, sugar and cornstarch in a small saucepan. Heat over medium heat until the sugar is melted. Continue to cook until the mixture is slightly thickened and the juices coat the back of a spoon, about 3-5 minutes.
- Bake: Pour the blueberry mixture into the crust. Top with reserved oat crumble mixture and bake.
Before You Make This
- Lightly spray the baking pan before adding your parchment paper. It helps the paper stay put while you press in the crust.
- Zest the lemon before squeezing it for the juice needed in this recipe. Once it's juiced, there's nothing left to zest.
- Need a gluten-free blueberry oat bar? Substitute the rolled oats with gluten-free oats and the all-purpose flour with a gluten-free flour blend (such as King Arthur Measure for Measure Gluten-Free Flour or Bob's Red Mill 1 to 1 Gluten-Free Baking Flour).
- Let them cool completely. Give them 2 ½ hours at room temperature so the filling sets up cleanly, just like a classic pie.
- Serving a crowd? You can double this recipe to make a 9x13" pan. The bars will be a little thicker and take a few minutes longer to bake.
Make Ahead and Storage
Fridge: These keep covered in the fridge for up to four days. The crumb topping will slowly soften as it absorbs moisture from the fruit.
Freezer: Layer cooled bars between sheets of parchment paper in an airtight container. They will keep for up to three months.
More Summer Fruit Desserts
Fresh produce makes summer desserts extra flavorful!
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Recipe
Blueberry Oat Crumble Bars
Ingredients
- 1¼ cups all-purpose flour
- 1 cup rolled oats
- ⅓ cup granulated sugar
- ⅓ cup brown sugar, packed
- 1 teaspoon baking powder
- ½ teaspoon ground cinnamon
- ½ teaspoon vanilla extract
- 8 tablespoons unsalted butter, melted
- 3½ cups blueberries
- zest of 1 lemon
- 1 tablespoon fresh lemon juice
- ¼ cup granulated sugar
- 1 tablespoon cornstarch
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Instructions
To make the crumble:
- Preheat oven to 350°F. Line an 8x8" square baking pan with enough parchment paper that so it hangs over the sides. (You'll use it as handles to lift the bars out of the pan later.)
- Stir together flour, oats, ⅓ cup granulated sugar, brown sugar, baking powder and cinnamon in a bowl. Stir in vanilla and butter. Reserve ⅓ of mixture (about 1 cup) in a small bowl and refrigerate. Press remaining mixture into bottom of prepared baking pan. Bake for 10 minutes. Set aside to cool slightly.1¼ cups all-purpose flour, 1 cup rolled oats, ⅓ cup granulated sugar, ⅓ cup brown sugar, , 1 teaspoon baking powder, ½ teaspoon ground cinnamon, ½ teaspoon vanilla extract, 8 tablespoons unsalted butter,
- While the crust is baking, add blueberries, lemon zest, lemon juice, ¼ cup granulated sugar and cornstarch to a small saucepan. Heat over medium heat and stir together until sugar is melted. Continue to cook for another 3-5 minutes or until the blueberry juices are slightly thickened and coat the back of a spoon.3½ cups blueberries, zest of 1 lemon, 1 tablespoon fresh lemon juice, ¼ cup granulated sugar, 1 tablespoon cornstarch
- Pour warm blueberry mixture into crust. Sprinkle with remaining oatmeal mixture from refrigerator. Bake for 35-45 minutes or until the edges bubble and the top is golden brown. Cool completely.
- When ready to serve, lift bars from the pan using parchment paper. Place on a cutting board and cut into 16 pieces.
Notes
- Fresh or frozen blueberries work equally well in this recipe. You'll need to cook them for longer in order to get the juices to thicken slightly.
- Use old-fashioned or rolled oats for the best results. Quick oats can be used in a pinch but the crumble will be softer. You can also swap in some chopped nuts or seeds for oats in the crumb mixture for extra crunch.
- Don't forget to zest the lemon before juicing it! (It's really hard to zest a squeezed lemon, speaking from personal experience.)
- Serving gluten-free guests? Swap out the all-purpose flour and rolled oats for gluten-free flour blend and gluten-free rolled oats.
- Lightly spray the baking pan before adding your parchment paper to help it stay in place easily.
- Let the bars cool completely before slicing. This allows the filling to fully set.
- These bars will keep in the fridge for up to 4 days and in the freezer for up to three months. If freezing, layer the bars between sheets of parchment paper.
- Serving a crowd? You can double this recipe to make a 9x13" pan. The bars will be a little thicker and take a few minutes longer to bake.
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Nutrition
Nutrition info not guaranteed to be accurate.
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