Preheat oven to 350° F. Mix flour, butter and powdered sugar with an electric mixer until the dough starts to come together.
Press into an ungreased 8 x 8 pan, building up an edge Bake 20 minutes, until light brown.
Wipe out bowl. Beat remaining ingredients for 3 minutes until light and fluffy. Pour over hot crust. Bake another 25 minutes longer, or just unitl no imprint remains when touched lightly in center.
Allow to cool completely, then sprinkly with powdered sugar and cut into squares.
