Preheat the oven to 375 F. Grease a 9×13 inch pan or line with parchment paper
In a medium bowl, stir together 1 cup sugar, 3 cups flour, and baking powder. Mix in salt and lemon zest
Use a fork or pastry cutter to blend in the butter and egg This can also be done in a food processor. Dough will be crumbly.
Pat half of dough into the prepared pan
In another bowl, stir together the sugar, cornstarch and lemon juice
Gently mix in the blueberries
Sprinkle the blueberry mixture evenly over the crust
Crumble remaining dough over the top
Bake in preheated oven for 45 minutes, or until top is slightly brown
Cool completely before cutting into squares
Notes
I prefer fresh blueberries in this recipe. If you are using frozen blueberries just thaw and drain them really well.
You can put them in the refrigerator if you need them to cool faster. You can slice them warm but they will be easier to handle and slice if they have cooled.