In a large bowl, whisk together instant pudding and milk for 2 minutes. Fold in the whipped topping.
In a 9×13-inch dish, layer graham crackers on the bottom, then spread half of the pudding mixture over them.
Add another layer of graham crackers, then the remaining pudding mixture, followed by a final layer of graham crackers.
Cover and refrigerate for at least 1 hour or up to 24 hours.
To make the ganache, heat the cream and butter in a saucepan until small bubbles form around the edges (do not boil).
Pour the hot cream over the chocolate chips and let sit for 10 minutes.
Stir the cream and chocolate together until smooth, then pour over the top graham cracker layer. Spread evenly.
Cover and chill for at least 8 hours or up to 2 days.
The longer it chills, the softer the graham crackers will become. Slice and serve.