Butter a 9x13 pan. Line with crackers. Mix pudding and milk, blend in Cool Whip. Pour 1/2 of the mixture over the crackers. Place 2nd layer of crackers over pudding. Pour remaining pudding, top with crackers. Refrigerate.
TOPPING: 2 ounces unsweetened chocolate, melted, 2 tsp. white corn syrup, 2 tsp. vanilla, 3 Tbs. butter, 1 1/2 cups of powdered sugar, 3 Tbs. milk Beat and spread over crackers. Refrigerate 24 hours before serving.