Preheat oven to 375°F (190°C). Line an 8x8 inch baking pan with parchment paper, leaving an overhang.
For the crust, combine flour and sugar in a bowl. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs.
Press about two-thirds of the crust mixture evenly into the bottom of the prepared pan.
Bake the crust for 12-15 minutes, or until lightly golden.
While the crust bakes, prepare the blueberry topping. In a medium bowl, toss blueberries with sugar, cornstarch, and lemon juice until evenly coated.
Pour the blueberry mixture over the partially baked crust and spread evenly.
Crumble the remaining crust mixture over the blueberries.
Bake for another 20-25 minutes, or until the topping is bubbly and the crumb topping is golden brown.
Let the bars cool completely in the pan on a wire rack before cutting into squares.
Notes
Store leftover bars in an airtight container at room temperature for up to 3 days, or in the refrigerator for longer storage.