Preheat oven at 375. In a mixing bowl, combine flour, sugars, baking powder, and baking soda. In another mixing bowl, combine egg whites, margarine, peanut butter, and vanilla. Mix dry ingredients with wet ingredients just until moistened. If necessary, cover and chill till easy to handle. Then, roll dough into 3 cm balls and place 5 cm apart on unprepared baking sheet. Using the tines of a fork dipped in additional sugar, flatten balls to about 1 cm thick by pressing fork in two directions to form crisscross marks. Bake for dozen minutes or until lightly brown. ----