Dissolve gelatin in 3/4 cup boiling water; set aside. Prepare cake mix using package directions. Bake in 13 x 9-inch baking dish. Cool for 20 to 25 minutes.
Pierce cake with fork at 1/2-inch intervals. Pour gelatin over cake. Place in refrigerator. Combine remaining ingredients in deep chilled bowl. Whip until stiff. Spread over cake. Refrigerate for several hours.
