For the crust: Combine flour and powdered sugar. Add butter (1 1/2 sticks, room temperature, cut into 1/2 inch cubes). Using back of fork blend until mixture resembles coarse meal. Press into 9x13 pan. Bake about 20 minutes.
Maintain oven temperature.
Meanwhile, beat eggs, sugar, lemon juice (about 5 or 6 lemons), grated lemon peel, and remaining flour in a bowl to blend.
Pour lemon mixture over hot crust. Bake until lemon layer is set, about 20 minutes. Cool completely.
Cut into squares. Sift powdered sugar over before serving.