Preheat oven to 375 F.
Combine sugar, brown sugar, baking powder, flour and salt in a large bowl.
In a small bowl mix the egg and vanilla extract. Add it to the flour mixture.
Add in the butter pieces and crumble them with your hands to form crumbs.
Press ¾ of the crumble into a parchment lined 8 x 8" Set aside the remaining ¼ while preparing the filling.
Prepare the filling by combining the blueberries, sugar, lemon juice and cornstarch in a bowl. Toss on top of the crust.
Crumble the remaining crust on top. Bake for 45 minutes until the blueberries burst and the crumbs are golden.