Line a 9x13 inch pan with graham crackers. Spread half of pudding mixture on crackers. Put on another layer of crackers, the rest of the pudding, then a top layer of crackers.
Bring cocoa, 1/4 cup milk, and sugar to a boil and cook one minute. Remove from stove and add butter and vanilla. Mix. Let cool slightly, about 5 minutes. Spread over top of dessert. Let set in refrigerator overnight.