1 small box of jello or other flavored gelatin
1 carton whipped topping
Mix and bake the cake mix according to packaging. Cool for 15-30 minutes. Poke holes every 1/2 inch of the cake using a fork. Mix gelatin using 1 cup boiling water until dissolved and 1/2 cup cold water. Carefully liquid gelatin over the entire cake. Make sure all of the holes you poked get some of the liquid in it. Chill for 3-4 hours.
Top with whipped topping.
You can use any flavor of cake and gelatin. For Phil's birthday I made white cake with peach jello and then cut a fresh peach for on top of the "frosting". We have also had Pineapple cake mix and orange jello.