Initial Preparation: Begin by ensuring that the 8-ounce container of frozen whipped topping is completely thawed. Allow the three cups of heavy cream and four ounces of cream cheese to reach room temperature until the cream cheese is sufficiently softened, which typically requires about 45 minutes. Meanwhile, prepare a 9x13-inch baking pan by lining it with two sheets of parchment paper. These sheets should be positioned perpendicular to each other, extending about two inches over all four sides of the pan to create a sling for easier removal of the dessert.
Layering the Base: Break eight of the full-size graham crackers in half. Arrange these pieces in a single layer at the bottom of the prepared pan, ensuring they are touching. It is not necessary for the crackers to completely cover the pan.
Marshmallow Layer: Place the cream cheese and the entire contents of the marshmallow crème jar into the bowl of a stand mixer (alternatively, a large bowl and an electric hand mixer may be used). Beat these ingredients with the paddle attachment on medium speed until the mixture is smooth and well combined, about 30 seconds. Incorporate two cups of the whipped topping into this mixture, folding gently until just combined. Dollop this marshmallow mixture onto the arranged graham crackers, spreading it into an even layer.
Chocolate Layer: Without needing to clean the bowl, combine the heavy cream with the instant chocolate pudding mix in the same mixing bowl. Whisk these together until the mixture is smooth and homogenous. Fold in the remaining one cup of whipped topping until just combined. Spread this chocolate pudding mixture evenly over the marshmallow layer.
Final Assembly: Break the remaining seven graham cracker sheets in half, and arrange these along with the remaining graham cracker half in a single layer over the chocolate pudding mixture. This completes the assembly of the layers.
Freezing: Cover the pan and place it in the freezer. Freeze the dessert until it is firm, which will take a minimum of six hours.
Serving: Once the dessert has set and is firm, use the overhanging parchment paper to lift the frozen slab out of the pan onto a cutting board. Cut the slab into 15 squares, using the graham crackers as a guide for even portions.