In a medium bowl, whisk together the sugar, baking powder, salt and flour. Cut in the butter using two knives or a pastry blender, until pieces are no larger than pea sized. Stir in the beaten egg to form a crumbly dough.
Pat 1/2 the dough in an even layer into the prepared pan.
In a medium bowl, whisk together the lemon zest and juice, 1/2 cup sugar, and the cornstarch. Toss the blueberries in the mixture and spread the blueberries on top of the dough in the pan.
Crumble the remaining dough evenly over the blueberries. Bake 45 to 50 minutes or until lightly browned.