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Horizontal image of a stack of fruit bar cookies on a wooden cutting in front of bowls of ingredients and a blue napkin.

Blueberry Oatmeal Squares

  • Author: Fanny Slater
  • Total Time: 3 hours, 30 minute
  • Yield: 12 squares 1x


Lemon zest adds a pop to these blueberry, brown sugar, and oatmeal squares. They’re perfect for breakfast, dessert, or a quick snack.


  • 3 cups fresh blueberries
  • 1/2 cup granulated sugar
  • 1 teaspoon vanilla extract
  • 3 tablespoons lemon juice (from about 1 large)
  • 4 teaspoons cornstarch
  • 2 tablespoons cold water
  • 2 1/2 cups rolled oats
  • 1 1/4 cups all-purpose flour
  • 3/4 cup packed light brown sugar
  • 1 tablespoon lemon zest (from about 1 large)
  • 1/4 teaspoon coarse salt
  • 1 1/4 teaspoons ground cinnamon
  • 2 sticks (1 cup) cold unsalted butter, cubed


  1. Preheat the oven to 350°F. Line an 8-inch square cake pan with parchment paper to create a sling for easy removal. Spray with non-stick cooking spray.
  2. In a medium saucepot over medium-high heat, add the blueberries, granulated sugar, vanilla, and lemon juice. Stir to combine. When the blueberries begin to release their juices, allow the liquid to come to a boil. Reduce the heat to medium-low and simmer, stirring occasionally, until the berries are broken down and tender, about 10 minutes.
  3. While the blueberries are cooking, whisk the cornstarch with the water until blended in a small bowl. Gradually stir the cornstarch slurry into the blueberry mixture and continue stirring until the mixture is visibly thickened, about 1 minute. Remove pot from heat. Transfer the blueberry mixture to a bowl and cool to room temperature on the counter. Then refrigerate until chilled, about 1 hour.
  4. In a large mixing bowl, stir the oats, flour, brown sugar, lemon zest, salt, and cinnamon together until combined. Using a pastry blender (or two butter knives), cut in the butter until the mixture has the texture of coarse crumbs.
  5. Firmly press half of the crumbs into the bottom of the prepared pan to create a smooth, even layer. Top with the blueberry filing, and then scatter the remaining oat mixture on top. Press down lightly to make sure it adheres.
  6. Bake until the edges are set and the top layer of crumbs is a light golden color, about 50-55 minutes. Remove from the oven and place on a wire rack.
  7. Cool completely in the pan, about 1 hour at room temperature, and then use the ends of the parchment paper to help lift the bars out of the pan. Slice into even squares and serve.
  8. Store leftover blueberry squares in an airtight container in the fridge for up to 1 week.
  • Prep Time: 25 minutes
  • Cook Time: 1 hour, 5 minutes
  • Category: Bars
  • Method: Stovetop/Baking
  • Cuisine: Snacks

Keywords: blueberry, oat, oatmeal, squares, bars