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Oat Flour Blueberry Crumble Squares – Simple, Cozy, and Naturally Sweet

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Prep Time 15 minutes
Cook Time 35 minutes
Total Time 50 minutes
Servings: 9 servings
Ingredients Method

Ingredients
  

  • For the crust and crumble:
  • 2 cups oat flour (store-bought or finely ground rolled oats)
  • 1 cup old-fashioned rolled oats
  • 1/2 cup light brown sugar, packed
  • 1/4 cup granulated sugar
  • 1/2 teaspoon fine sea salt
  • 1/2 teaspoon ground cinnamon (optional)
  • 1/2 teaspoon baking powder
  • 10 tablespoons unsalted butter, melted and slightly cooled
  • 1 teaspoon vanilla extract
  • For the blueberry filling:
  • 3 cups blueberries (fresh or frozen; no need to thaw)
  • 2 tablespoons lemon juice
  • 1 teaspoon lemon zest
  • 1/3 cup granulated sugar (adjust to berry sweetness)
  • 2 tablespoons cornstarch
  • 1 teaspoon vanilla extract
  • Pinch of salt

Method
 

  1. Preheat the oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving overhang for easy lifting. Lightly grease the sides.
  2. Make the crust and crumble: In a large bowl, whisk oat flour, rolled oats, brown sugar, granulated sugar, salt, cinnamon, and baking powder. Pour in melted butter and vanilla. Stir until the mixture looks like damp sand and clumps when pressed.
  3. Form the base: Transfer about 2/3 of the mixture to the pan. Press it firmly and evenly into a compact crust. Use the bottom of a measuring cup to pack it well.
  4. Mix the filling: In another bowl, toss blueberries with lemon juice, zest, sugar, cornstarch, vanilla, and a pinch of salt until evenly coated.
  5. Assemble: Spread the blueberry mixture over the crust in an even layer. Sprinkle the remaining crumble over the top, squeezing some of it into larger clumps for texture.
  6. Bake for 40–50 minutes, until the top is golden and the filling is bubbling around the edges. If using frozen berries, add 5 minutes.
  7. Cool completely in the pan on a rack—at least 2 hours. This sets the filling so the squares slice cleanly.
  8. Lift out using the parchment and cut into 12–16 squares. Serve as is or with a spoonful of yogurt or ice cream.