Jello Ice Box Cake
I have made this for years.

1 box yellow cake mix
1 box any flavor jello
1 box instant vanilla pudding
1 small container Cool Whip
1 teaspoon vanilla

Bake cake as directed in a 9x13 pan. Mix jello as directed and let stand at room temp. Mix pudding as directed. Fold in cool whip and vanilla, chill. After cake is done, poke holes all over and pour jello over cake while hot. Let cool, then top with the pudding mixture.