Prepare the crust: Preheat oven to 350* F. Combine two cups flour with the powdered sugar. Cut in butter or margarine and stir until mixture resembles coarse crumbs. Press into an 8×13 baking dish and bake for 20-25 minutes, or until edges being to brown slightly.
While the crust is baking, prepare the filling. Beat the eggs together with the sugar, lemon juice and zest, flour and baking powder until well combined.
Once the crust is baked pour the filling over the crust and return to the oven for 25 minutes or until the filling is set. Sprinkle with additional powdered sugar and allow pan to cool completely before cutting into squares.