Make pudding with milk, and fold into cool whip. Butter bottom and sides of 9 x 13 pan. Line bottom with WHOLE graham crackers. Put layer of pudding over crackers, then add another layer of graham crackers. One more layer of pudding, then a final layer of graham crackers (you will have 3 layers of crackers, 2 layers of pudding). Refrigerate for 2 hours.
2 1oz squared unsweetened chocolate, melted
2 tsp light corn syrup
2 tsp vanilla
3 Tbs soft margarine
1 ½ C sifted powdered sugar
3 Tbs milk
Combine above ingredients and beat until smooth. Spread over cake, refrigerate 24 hours before serving.