Prep the pan and oven: Heat the oven to 350°F (175°C). Line an 8-inch square baking pan with parchment, leaving overhang for easy lifting. Lightly grease the parchment.

Make the blueberry filling: In a bowl, toss 2 1/2 cups blueberries with 1 1/2 tablespoons cornstarch, 1 tablespoon lemon juice, 1 teaspoon lemon zest, and 1–2 tablespoons maple syrup. If using frozen berries, do not thaw; add 1 extra teaspoon cornstarch.

Mix the dry base/crumble: In a large bowl, combine 1 3/4 cups rolled oats, 1 cup almond flour, 1/3 cup protein powder, 1/4 teaspoon salt, and 1/2 teaspoon cinnamon. Stir well to break up any clumps.

Add wet ingredients: Melt 1/3 cup coconut oil (or butter) and let it cool slightly. Stir in 1/4 cup maple syrup, 1/3 cup unsweetened applesauce, and 1 teaspoon vanilla. Pour over the dry ingredients and mix until the mixture is evenly moistened and crumbly.

Sweeten the crumble (optional): For a more classic bakery-style top, sprinkle in 2 tablespoons brown sugar and toss. This helps the crumble brown and crisp.

Press the base: Transfer about 2/3 of the oat mixture into the pan. Press it firmly into an even layer. Use the bottom of a measuring cup to pack it tight so it holds together after baking.

Add the blueberries: Spread the blueberry mixture evenly over the base. If the filling looks dry, sprinkle on a teaspoon of water; if it looks too wet, dust a pinch more cornstarch.

Crumb the top: Scatter the remaining oat mixture evenly over the berries, leaving some bigger clumps for texture.

Bake: Place the pan in the center of the oven. Bake 32–38 minutes, until the top is golden and the blueberry juices bubble along the edges.

Cool completely: Let the bars cool in the pan for at least 1 hour, then chill for another 30–60 minutes. This step sets the filling so the bars slice cleanly.

Slice and serve: Use the parchment to lift the slab out. Cut into 12 bars for snacks or 9 for larger portions. Enjoy at room temperature or slightly chilled.