Heat oven to 350~. Mix 1 cup flour, margarine and powdered sugar. Press in ungreased baking pan, 8x8", or 9x9", building 1/2 up sides. Bake 20 minutes. Beat remaining ingredients until light and fluffy, about 3 minutes; pour over the baked layer. Bake until no indentation remains when touched in the center, about 25 minutes. Cool. Sprinkle with more powdered sugar if desired. Cut into squares. ----