Cream butter and 1/2 cup powdered sugar; add 2 cups flour, beating well. Press pastry into a lightly greased 15-x 10-x 1-inch jellyroll pan. Bake at 350° for 15 minutes or until lightly browned.
Combine eggs and sugar; beat well. Add 1/4 cup flour, baking powder, salt, lemon rind, and juice, beating well. Pour over baked crust.
Bake at 350° for 25 minutes or until lightly browned. Let cool, and cut into 1 1/2-inch squares. Sprinkle with additional powdered sugar.