Line the bottom of a 9x13" pan with graham crackers. Set aside.

Prepare the pudding with the milk according to the package directions. While the pudding is setting, whip the heavy cream until medium peaks form. Fold the whipped cream into the pudding mixture.

Carefully spread half of the pudding mixture over the graham crackers. Add another layer of graham crackers and pour the remaining pudding mixture over the graham crackers and top the pudding with a final layer of graham crackers.

In a medium microwave-safe mixing bowl, melt the butter and add the cocoa powder, vanilla, powdered sugar, and milk. Whip until light and fluffy. Heat for 20 seconds on 50% power in the microwave, so it's very soft and shiny but not quite liquid. Gently spread over the top layer of graham crackers, cover with foil, and refrigerate for at least 8 hours. Cut into squares and serve.