Peanut Butter Blueberry Crumble Bars

Quick Recipe Version (TL;DR)

• Yield: 16 bars
• Prep Time: 20 minutes
• Cook Time: 35 minutes
• Total Time: 3 hours (includes cooling)

Quick Ingredients

• 1 1/2 cups (150 g) old-fashioned rolled oats
• 1 cup (125 g) all-purpose flour
• 3/4 cup (150 g) packed light brown sugar, divided
• 1/4 + 1/4 cup (100 g total) granulated sugar, divided
• 1/2 cup (115 g) unsalted butter, melted
• 2/3 cup (130 g) creamy peanut butter, divided
• 1 cup (130 g) roasted unsalted peanuts, roughly chopped
• 2 1/2 cups (375 g) blueberries (fresh or frozen)
• 1/3 cup (110 g) blueberry jam or preserves
• 1 1/2 Tbsp (12 g) cornstarch
• 1 Tbsp (15 ml) lemon juice, 1 tsp vanilla, 3/4 tsp fine salt

Do This

• 1. Preheat oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving overhang.
• 2. Stir oats, flour, 1/2 cup brown sugar, 1/4 cup sugar, 1/2 tsp salt, and 1/2 tsp baking powder. Add melted butter and 1/3 cup peanut butter; mix into damp crumbs. Stir in half the chopped peanuts.
• 3. Press about 2/3 of the crumb mixture firmly into the pan as the base; reserve the rest for topping.
• 4. Toss blueberries with remaining 1/4 cup sugar, remaining 1/4 cup brown sugar, cornstarch, lemon juice, vanilla, and pinch of salt. Fold in blueberry jam.
• 5. Spread blueberry mixture over crust. Warm remaining 1/3 cup peanut butter slightly and drizzle over berries. Sprinkle with remaining crumb mixture and remaining peanuts.
• 6. Bake 35 minutes, until top is golden and berries are bubbling. Cool completely 2 to 2 1/2 hours before lifting out and slicing into bars.

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Why You’ll Love This Recipe

• Buttery, peanutty oat base and crumble topping wrapped around a juicy, jammy blueberry layer.
• Perfectly sturdy bars that slice cleanly yet stay soft and chewy in the center.
• Easily made with fresh or frozen blueberries, plus pantry staples you probably already have.
• Ideal for make-ahead snacks, lunchbox treats, or a rustic dessert for guests.

Grocery List

• Produce: Fresh or frozen blueberries, 1 lemon.
• Dairy: Unsalted butter.
• Pantry: Old-fashioned rolled oats, all-purpose flour, light brown sugar, granulated sugar, creamy peanut butter, roasted unsalted peanuts, blueberry jam or preserves, cornstarch, vanilla extract, fine sea salt, baking powder.

Full Ingredients

For the Peanut-Oat Base & Crumble Topping

• 1 1/2 cups (150 g) old-fashioned rolled oats
• 1 cup (125 g) all-purpose flour
• 1/2 cup (100 g) packed light brown sugar
• 1/4 cup (50 g) granulated sugar
• 1/2 tsp baking powder
• 1/2 tsp fine sea salt
• 1/2 cup (115 g) unsalted butter, melted and slightly cooled
• 1/3 cup (85 g) creamy peanut butter (stirred if natural)
• 1 cup (130 g) roasted unsalted peanuts, roughly chopped, divided

For the Jammy Blueberry Peanut Layer

• 2 1/2 cups (375 g) blueberries, fresh or frozen (do not thaw)
• 1/4 cup (50 g) granulated sugar
• 1/4 cup (50 g) packed light brown sugar
• 1 1/2 Tbsp (12 g) cornstarch
• 1 Tbsp (15 ml) freshly squeezed lemon juice
• 1 tsp vanilla extract
• 1/4 tsp fine sea salt
• 1/3 cup (110 g) blueberry jam or preserves
• 3 Tbsp (45 g) creamy peanut butter, gently warmed for drizzling

Optional Finishing Touches

• Flaky sea salt, for sprinkling on top after baking
• Extra chopped roasted peanuts, for garnish

Step-by-Step Instructions

Step 1: Prep your pan and preheat the oven

Set an oven rack in the center position and preheat the oven to 350°F (175°C).

Line an 8-inch (20 cm) square baking pan with parchment paper, leaving a generous overhang on two opposite sides to create a sling. This makes it much easier to lift the bars out cleanly later. Lightly grease any exposed sides of the pan with butter or a bit of oil to prevent sticking.

Step 2: Make the peanut-oat base and crumble

In a large mixing bowl, combine the oats, flour, 1/2 cup brown sugar, 1/4 cup granulated sugar, baking powder, and 1/2 teaspoon salt. Stir until everything is evenly blended and there are no streaks of flour.

Pour in the melted butter and add 1/3 cup peanut butter. Stir with a fork or spatula until the mixture turns into moist, clumpy crumbs that hold together when squeezed. Add half of the chopped peanuts (about 1/2 cup) and fold them in evenly.

Measure out about 2 firmly packed cups of this mixture (roughly 2/3 of it) and set aside the remaining 1/3 for the crumble topping.

Step 3: Press the base into the pan

Transfer the larger portion of the crumb mixture to your prepared pan. Use your fingers or the bottom of a measuring cup to press it firmly and evenly into the bottom. Aim for a level surface with no loose crumbs, especially in the corners and along the edges, so the bars hold together well once sliced.

If the mixture sticks to your fingers, lightly dampen your fingertips or use a small piece of parchment as a barrier. Set the pan aside while you prepare the blueberry layer.

Step 4: Mix the jammy blueberry layer

In a medium bowl, combine the blueberries, 1/4 cup granulated sugar, 1/4 cup brown sugar, cornstarch, lemon juice, vanilla, and 1/4 teaspoon salt. Toss gently until the berries are evenly coated and no dry cornstarch is visible. The mixture will look a bit powdery at first; that is fine.

Add the blueberry jam and fold it through the berries. You should have a glossy, slightly thick mixture with small pockets of jam. The cornstarch will thicken the blueberry juices as the bars bake, turning the center into a soft, jammy layer rather than something runny.

Step 5: Assemble the layers

Pour the blueberry mixture over the pressed crust and spread it into an even layer, nudging berries into the corners.

Gently warm the remaining 3 tablespoons peanut butter in a microwave-safe bowl for about 10–15 seconds, just until fluid enough to drizzle. Using a spoon, drizzle the peanut butter over the blueberries in thin ribbons; it does not need to be perfect, a rustic swirl is ideal.

Sprinkle the reserved crumb mixture evenly over the top, leaving some blueberries peeking through for a pretty, rustic look. Finish by scattering the remaining 1/2 cup chopped peanuts over the crumble.

Step 6: Bake until golden and bubbly

Place the pan in the preheated 350°F (175°C) oven and bake for 35–40 minutes. The top should be a deep golden brown, and the blueberry layer should be visibly bubbling around the edges and in a few spots toward the center.

If the top is browning too quickly before the filling bubbles, loosely tent the pan with a piece of foil and continue baking until the filling is clearly thick and jammy.

Step 7: Cool completely and slice

Remove the pan from the oven and place it on a wire rack. If using, lightly sprinkle a pinch or two of flaky sea salt over the hot crumble for a sweet-salty finish.

Allow the bars to cool completely in the pan, at least 2 to 2 1/2 hours. The filling will set as it cools; if you cut too soon, it will be messy and soft. Once cool, use the parchment sling to lift the entire slab out of the pan onto a cutting board. Use a sharp knife to cut into 16 squares (4 by 4) or larger rectangles, wiping the knife between cuts for the cleanest edges.

Pro Tips

• Use old-fashioned oats: Quick oats will make the crust denser and less textured. Old-fashioned rolled oats give the best chewy-crisp crumble.
• Frozen blueberries are fine: If using frozen, do not thaw them first. Toss them in straight from the freezer so the layer does not become watery.
• Cool completely for neat bars: These are much easier to slice once fully cool and set. If you are in a hurry, you can chill the pan in the fridge for 45–60 minutes after an initial 20 minutes of cooling at room temperature.
• Adjust sweetness with your jam: A very sweet jam will make the bars sweeter overall. For a slightly tarter bar, use a lower-sugar jam or reduce the granulated sugar in the filling by 1–2 tablespoons.
• Line with a parchment sling: That overhang is the difference between frustration and perfectly intact bars. Do not skip it.

Variations

• Mixed berry crumble bars: Swap some or all of the blueberries for raspberries, blackberries, or chopped strawberries and use a mixed berry jam.
• Almond or cashew twist: Replace the peanut butter with almond or cashew butter and use sliced almonds or chopped cashews instead of peanuts.
• Chocolate-peanut blueberry bars: Sprinkle 1/2 cup (85 g) dark chocolate chunks over the blueberry layer before adding the crumble topping for a chocolatey, peanut-butter-and-jelly vibe.

Storage & Make-Ahead

Once completely cooled and sliced, store the bars in an airtight container.

At room temperature, they keep well for about 2 days, especially in a cool kitchen. For longer storage, refrigerate them for up to 5 days. Place parchment or wax paper between layers to prevent sticking.

For freezing, arrange bars in a single layer on a sheet pan and freeze until solid, then transfer to a freezer bag or airtight container, separating layers with parchment. They will keep for up to 2–3 months. Thaw overnight in the fridge or at room temperature for 1–2 hours.

These bars are perfect for making ahead. Bake a day before serving for the easiest slicing and the best set texture.

Nutrition (per serving)

Approximate values for one bar (1 of 16): about 290 calories, 16 g fat, 6 g protein, 33 g carbohydrates, 3 g fiber, and 18 g sugars. These values are estimates and will vary based on the exact brands and ingredients you use.