Lemon Pillow Cake 1 (18.25 ounce) box white cake mix 1 can lemon pie filling Mix cake as directed on box and pour batter into a 9 x 13-inch pan. Place spoonsful of lemon pie filling over the batter. Bake as directed on the box. Let cool completely. Frosting 1 can ready-to-spread lemon flavored frosting 1 container Cool Whip Mix frosting and Cool Whip together and spread on cake. Store in the refrigerator.