Combine the flour, butter and powdered sugar until well blended.
Press the dough into a greased 8x8 baking dish.
Bake for 20 minutes.
Make the Filling
While the crust is baking, make the filling.
Beat the eggs, salt, granulated sugar, baking powder and lemonade starter using an electric mixer. Continue beating for 3-4 minutes, until the mixture is light and fluffy.