Step 1: Prepare the Pudding Mixture

In a large bowl, whisk together 2 cups whole milk and 2 packages instant vanilla pudding mix for 2 minutes until well combined. Fold in 1 thawed container (8 ounces) of frozen whipped topping using a rubber spatula until everything is evenly mixed and no streaks remain.

Step 2: Build the Cake Layers

Pour the pudding mixture aside temporarily. In a 13×9-inch baking dish, arrange a single layer of graham crackers evenly across the bottom, breaking crackers as needed to fill any gaps. Spread half of the prepared pudding mixture evenly over the first layer of graham crackers. Add a second layer of graham crackers over the pudding, then spread the remaining pudding mixture evenly over this second cracker layer. Top with a final layer of graham crackers.

Step 3: Add the Chocolate Frosting

Allow the chocolate frosting to come to room temperature if using store-bought frosting directly from the refrigerator. This makes it easier to spread without tearing the graham crackers. Spread the frosting evenly over the top layer of graham crackers, covering completely.

Step 4: Chill and Set

Cover the baking dish tightly with plastic wrap or aluminum foil to prevent refrigerator odors from being absorbed into the cake. Refrigerate for a minimum of 3 hours, though overnight chilling is recommended. The longer the cake chills, the softer the graham crackers become, creating a more cake-like texture.

Step 5: Serve

Once thoroughly chilled and set, cut the cake into square portions using a sharp knife. Serve chilled directly from the refrigerator. Store any leftovers covered in the refrigerator for up to 4 days.