1: Preheat the oven to 375 degrees F (190 degrees C).
2: Grease a 9×13 inch pan.
3: In a medium bowl, stir together 1 cup sugar, 3 cups flour, baking powder, salt, and lemon zest.
4: Use a fork or pastry cutter to blend in the butter and egg until dough is crumbly.
5: Pat half of the dough into the prepared pan.
6: In another bowl, stir together the sugar, cornstarch, and lemon juice.
7: Gently mix in the blueberries.
8: Sprinkle the blueberry mixture evenly over the crust.
9: Crumble the remaining dough over the berry layer.
10: Bake in the preheated oven for 45 minutes, or until the top is slightly brown.
11: Cool completely before cutting into squares.
