What you'll need:
White cake made according to directions
Small box of jello mixed according to directions
1 pint Whipping Cream
1 t Vanilla
1/2 C Powdered Sugar
OR you can go completely old school and use Cool Whip.
Make the cake according to directions in a 13x9 pan. Cool. Poke holes all over the top with a fork. Mix jello with water according to box and pour over the top of the cake.