Cream butter; gradually add powdered sugar, beating until light and fluffy. Stir in flour. (Mixture will be stiff.) Press into a 15x 10x 1-inch jellyroll pan; prick all over with a fork. Chill 30 minutes. Bake at 375 degrees for 5 minutes; reduce heat to 300 degrees, and bake an additional 20 minutes or until golden brown. Cut into squares or diamond shapes while warm, and sprinkle with ----