combine the sugars, baking powder, flour and salt in a bowl. Add in the egg and vanilla extract. Add in the butter and crumble everything together with your fingers. Press 3/4 of the crumbs topping into the bottom of a 9 x 9 pan fitted with parchment paper. Mix the filling ingredients together and pour on top of the crust. Crumble the remaining crumbs on top of the filling. Bake at 350 F for 45 minutes. Cool completely before slicing.