Preheat the oven to 375 degrees F. Line a 9×13 inch pan with parchment paper and spray with nonstick cooking spray.

In a medium bowl, stir together 1 cup sugar, 3 cups flour, salt, lemon zest and baking powder.

In a small bowl, whisk the egg and vanilla together until combined.

Use pastry cutter or your food processor to blend the flour mixture with the butter and egg/vanilla mixture. Dough will be crumbly. Pat half of dough into the prepared pan.

In another bowl, stir together ½ sugar and cornstarch. Gently mix in the blueberries. Sprinkle the blueberry mixture evenly over the crust. Crumble remaining dough over the berry layer.

Bake in preheated oven for 45 minutes, or until top is slightly brown. Cool completely before cutting into squares.