Blueberry Crumb Bars (Buttery, Jammy & So Simple)
These Blueberry Crumb Bars have a buttery shortbread-like base, juicy blueberry filling, and a golden oat crumb topping. They’re sturdy enough to hold, soft and jammy in the center, and perfect for picnics, potlucks, or a sweet treat with coffee.
Ingredients
- 3 cups all-purpose flour 375 g; fluff, then spoon and level for accuracy
- 1 cup old-fashioned rolled oats 100 g; for a rustic crumble texture
- 1 cup granulated sugar 200 g; for the crust and topping
- 1/2 cup light brown sugar 100 g; packed
- 1 teaspoon baking powder
- 1/2 teaspoon fine sea salt
- 1 teaspoon ground cinnamon optional, but cozy with blueberries
- 1 cup unsalted butter 2 sticks / 226 g; melted and slightly cooled
- 1 large egg lightly beaten
- 1 1/2 teaspoons vanilla extract for the crumb crust and topping
- 4 cups blueberries about 600 g; fresh or frozen, do not thaw if frozen
- 1/2 cup granulated sugar 100 g; for the blueberry filling
- 2 tablespoons lemon juice fresh is best
- 2 teaspoons lemon zest about 1 medium lemon
- 3 tablespoons cornstarch use 4 tablespoons if using frozen berries, or more if berries are very juicy
- 1 teaspoon vanilla extract for the blueberry filling
- salt pinch, for the blueberry filling
Instructions
- Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving overhang on the long sides to lift the bars out later. Lightly coat the parchment and pan sides with cooking spray or a thin layer of butter.
- In a large bowl, whisk together the flour, rolled oats, 1 cup (200 g) granulated sugar, light brown sugar, baking powder, 1/2 teaspoon salt, and cinnamon (if using). Break up any clumps of brown sugar with your fingers. This mixture will serve as both the base crust and crumb topping.3 cups all-purpose flour, 1 cup old-fashioned rolled oats, 1 cup granulated sugar, 1/2 cup light brown sugar, 1 teaspoon baking powder, 1/2 teaspoon fine sea salt, 1 teaspoon ground cinnamon
- Pour the melted butter, beaten egg, and 1 1/2 teaspoons vanilla extract over the dry mixture. Stir with a sturdy spoon or spatula until everything is evenly moistened. The mixture should look like coarse, sandy crumbs that clump slightly when pressed in your hand.1 cup unsalted butter, 1 large egg, 1 1/2 teaspoons vanilla extract
- Transfer about two-thirds of the crumb mixture to the prepared pan. Use your hands or the bottom of a measuring cup to press it into a firm, even layer, making sure to press well into the corners. This forms the buttery shortbread-like base that will help the bars hold together when sliced.
- In another bowl, combine the blueberries, 1/2 cup (100 g) granulated sugar, lemon juice, lemon zest, cornstarch, 1 teaspoon vanilla extract, and a pinch of salt. Gently toss until the berries are evenly coated and no dry cornstarch remains. If using frozen berries, work quickly so they don’t release too much juice before baking.4 cups blueberries, 1/2 cup granulated sugar, 2 tablespoons lemon juice, 2 teaspoons lemon zest, 3 tablespoons cornstarch, 1 teaspoon vanilla extract, salt
- Spoon the blueberry filling evenly over the pressed crust, spreading the berries and their juices right into the corners so every bar has a jammy center.
- Sprinkle the remaining crumb mixture evenly over the blueberries. Leave some larger clumps and some smaller bits for varied texture. Gently pat the crumbs so they adhere, but do not press them firmly like the base.
- Bake on the center rack for 40–50 minutes, or until the top is light golden brown and the blueberry filling is bubbling around the edges. If your oven runs hot, start checking around 38–40 minutes.
- Transfer the pan to a cooling rack and let the bars cool completely, at least 2 hours. The blueberry layer will continue to thicken as it cools. For the cleanest slices, chill the pan in the refrigerator for 1–2 hours after it reaches room temperature.
- Use the parchment overhang to lift the slab of blueberry crumb bars onto a cutting board. Slice into about 16 large or up to 24 smaller bars. Serve at room temperature, or slightly warm with a scoop of vanilla ice cream if desired.
Notes
Storage: Store bars in an airtight container at room temperature for up to 2 days, or refrigerate for up to 5 days. For longer storage, freeze on a baking sheet until solid, then transfer to an airtight container or freezer bag for up to 3 months.
From frozen: Thaw in the refrigerator overnight or at room temperature for 30–45 minutes. Warm individual bars briefly in the microwave (10–15 seconds) or in a 300°F (150°C) oven for 5–8 minutes if you like them warm.
Tips: The thickness of the base affects texture—press more firmly for a cookie-like base, or reserve a bit more dough for extra crumble on top. Cornstarch is key for a thick, jammy blueberry layer; if your berries are very juicy, add a little extra. Let the bars cool fully before slicing for neat squares. A light-colored metal pan bakes more evenly than glass, which can brown the edges faster.
Variations: Swap in up to half raspberries or blackberries for mixed berry crumb bars. Use 1 1/2–2 cups blueberry jam instead of fresh fruit for quick jam bars. Make gluten-free bars with a 1:1 gluten-free flour blend and certified gluten-free oats. Add more lemon zest and/or a lemon glaze for lemon–blueberry bars, or stir 1/2 cup chopped nuts into the topping for extra crunch.
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