How to Make It
Prepare the filling by combining pudding mix and milk. Beat. Stir in Cool Whip.
Place a layer of graham crackers in bottom of a 9x13 dish. Spread 1/2 filling mixture on top. Repeat with another layer of graham crackers, add rest of filling, top with final layer of graham crackers.
To make the topping, bring cocoa, milk and sugar to a roiling boil. Let topping boil for one full minute, stirring frequently.
Remove from heat, cool 1 minute.
Add butter and vanilla to topping, and stir till butter is melted.
Pour chocolate topping over graham crackers and refrigerate overnight.