Coat 2 large baking sheets with cooking spray, and dust with 1 tablespoon flour; set aside.
Combine sugar, cornstarch, margarine, and egg in a large bowl; stir well with a wire whisk. Scrape seeds from vanilla bean; add seeds to sugar mixture, reserving bean for another use. Add 3/4 cup flour, baking powder, and salt; stir until smooth.
Drop dough by rounded teaspoonfuls 2 inches apart onto prepared baking sheets. Bake at 350° for 15 minutes. Remove cookies from pan; let cool on wire racks.