Combine 2 cups flour and 1/2 cup powdered sugar; add butter, mixing well. Press mixture evenly into a 13- x 9- x 2-inch baking dish. Bake at 350° for 20 minutes.
Combine eggs, sugar, and lemon juice in a medium mixing bowl; beat well. Sift together 1/4 cup flour and baking powder in a medium mixing bowl; stir into egg mixture. Pour over baked crust. Bake at 350° for 25 minutes or until lightly browned and set. Sprinkle lightly with additional powdered sugar. Cool and cut into 1-inch squares.