1Heat oven to 350°F. In medium bowl, mix crust ingredients. Firmly press in bottom of ungreased 13x9-inch pan. Bake 10 minutes or until browned. Cool 15 minutes.
2Spoon 4 cups of the ice cream over cooled crust, spreading evenly. Spoon 1/3 cup of the hot fudge topping into small microwavable bowl; cover and refrigerate. Microwave remaining topping in uncovered jar on High 1 minute or until softened. Stir topping; spoon and spread over ice cream in crust. Spoon and spread remaining 4 cups ice cream over topping. Freeze until firm, 4 hours or overnight.
3Set oven control to broil. Top dessert evenly with marshmallows. Broil 1 to 2 minutes or until marshmallows are lightly browned. Freeze cake 3 hours.
4Before serving, microwave reserved 1/3 cup hot fudge topping uncovered on High 10 seconds. Stir; drizzle topping over dessert. Let stand 5 minutes before serving.