(Just a word of warning, it is messy to serve, and so not the prettiest looking dessert.)
11 whole graham crackers (approximately)
1 (3.5 oz) box instant vanilla pudding mix
2 cups milk
1 (8 oz) tub Cool Whip (Lite is fine)
1/4 cup milk
1/3 cup unsweetened cocoa powder
1 cup white sugar
2 tablespoons butter
1 teaspoon vanilla extract
Use an 8 inch square pan. Line the bottom of the pan with a single layer of graham crackers, breaking the crackers as needed to completely fill the pan. Combine pudding and milk, whisking for two minutes until combined and starting to set. Whisk in Cool Whip. Pour half the pudding mixture over the graham crackers. Lay out another layer of graham crackers. Repeat pudding and graham cracker layers. Put in the refrigerator.
Meanwhile, combine the milk, cocoa powder and sugar in a small saucepan. Heat until mixture is boiling, stir for one minute, then remove from heat. Add butter and vanilla, stir until mixed. Pour over graham crackers and return to refrigerator.
Keep in refrigerator for 24 hours before serving.