Bring the cocoa, sugar and milk to a boil.

Remove from heat, add the butter and vanilla, and set aside.

Mix the vanilla pudding and milk, then add the cool whip.

In a 9X13 dish, put a layer of Graham crackers on the bottom, then add half the filing.

Add another layer of Graham crackers, then the rest of the filling,, then top with the chocolate topping.

Refrigerate until cool, and serve.