In medium-size bowl, sift together flour, baking powder, and salt. In separate bowl, cream margarine; add sugar gradually and continue creaming until light. Add egg, vanilla, and Sweet ‘N Low; beat well. Thoroughly stir in dry ingredients. Refrigerate one hour. Preheat oven to 400F. Spray cookie sheets with nonstick coating agent.* Roll dough into 3/4-inch balls. Place 2 inches apart on prepared cookie sheets; press flat with base of floured glass. Flute edges with fork. Bake 6 to 8 minutes, or until brown. *There’s no need to spray with a nonstick coating agent if you own a nonstick cookie sheet.