Scottish Shortbread Cookies

Preheat oven to 275F. Place sugars in food processor and process until very fine. Add butter; pulse until sugar disappears. Add flour; pulse until no dry flour particles remain. (Mixture will be moist and crumbly.) Place in plastic bag and press together to form dough; knead lightly until dough holds together. Remove from bag. Shape dough into i-inch balls, Place on unbuttered cookie sheets 2 inches apart. Flatten each with a cookie press, fork. or the bottom of a glass lightly moisened with water. Bake 45 minutes to 1 hour or until pale golden. Remove from cookie sheets; cool completely on wire racks. Yields: about 4 dozen.