Line a 9 by 5-inch loaf pan with plastic wrap, letting the ends of the plastic wrap overhang the pan by 6 inches. Break one of the crackers into 4 pieces along the dotted lines.
Spread one side of 1 whole graham cracker and 1 graham piece with 1/2 cup of the marshmallow cream and lay in the loaf pan, cream side up. Spoon the softened chocolate ice cream over the crackers and smooth the top.
Coat both sides of another whole cracker and 1 piece using 1 more cup marshmallow cream and lay over the chocolate ice cream. Spoon the softened vanilla ice cream over the crackers and smooth the top.
Spread the remaining whole cracker and 1 more piece with the remaining 1/2 cup marshmallow cream. Lay the crackers over the vanilla ice cream, marshmallow side down. Wrap the pan tightly with plastic wrap and freeze until firm, about 6 hours.
To serve, unwrap and gently tug at the overhanging plastic wrap to remove the loaf from the pan. (If necessary, dip the bottom of the pan into hot water.) Using the plastic wrap to handle the loaf, invert it onto a serving platter. Peel away and discard the plastic wrap. Allow the cake to sit at room temperature for a few minutes before slicing. Serve with the hot fudge sauce.
**Note: To soften ice cream, scoop ice cream into a large mixing bowl. Use a large rubber spatula or wooden spoon to break up the ice cream. Stir and fold to create a smooth consistency.