Old-Fashioned Shortbread Cookie 1 cup butter, softened 3/4 cup sifted confectioners’ sugar 1/4 cup cornstarch 1 3/4 cups all-purpose flour Beat butter with electric mixer, medium speed. Gradually add confectioners’ sugar and cornstarch, beating well. Stir in flour until well combined. Firmly press dough into a lightly greased and floured 9-inch cookie mold or cake pan. Bake at 325 degrees F for 30 to 35 minutes. Invert cookie from pan and let cool on wire rack. Yields 1 (9-inch) cookie.