Line bottom of 13x9" dish with graham crackers.
In a bowl, mix pudding with milk as directed on pudding box; add Cool Whip to pudding, mix well. Pour pudding mix over graham crackers.
Add another layer of graham crackers over the pudding. Heat the can of frosting in the microwave until it is soft and easy to pour, about 30 seconds or so. Pour over the top layer of graham crackers.
Chill four hours or overnight.