Combine first 3 ingredients in a bowl.
Beat margarine at medium speed of an electric mixer until light and fluffy. Gradually add sugar, beating until well blended. Add vanilla and egg white; beat well. Add flour mixture, and stir until well blended. Turn dough out onto wax paper; shape into a 6- inch log. Wrap log in wax paper; freeze 3 hours or until very firm.
Preheat oven to 350°.
Cut log into 24 (1/4-inch) slices, and place slices 1 inch apart on a baking sheet coated with cooking spray. Bake at 350° for 8 to 10 minutes. Remove from sheet; cool on wire racks.