Make Hot Fudge Sauce: Place the marshmallows and cream in a saucepan over medium heat. Cook, stirring constantly, for 2 to 3 minutes or until marshmallows are semi-melted. Add chocolate. Cook, stirring constantly, until mixture is smooth and combined. Transfer to a bowl. Set aside for 1 hour to cool and thicken.
Meanwhile, make Chocolate Mousse: Place the chocolate and 3⁄4 cup of cream in a microwave-safe bowl. Microwave on HIGH (100%), stirring every 30 seconds, for 1 to 2 minutes or until chocolate is melted and smooth. Set aside for 1 hour to cool.
Meanwhile, make Marshmallow Cream: Place the marshmallows and cream in a saucepan over medium heat. Cook, stirring constantly, for 3 to 4 minutes or until smooth and combined. Transfer to a bowl. Set aside for 45 minutes or until cool. Fold in whipped cream.
Preheat oven to 190C/170C fan-forced. Line a large baking tray with baking paper. Trim 4cm off the top of cob. Leaving a 1cm thick edge, remove bread from centre of cob. Set cob aside. Tear bread and bread top into large pieces. Transfer to a bowl. Drizzle with melted butter. Toss to coat. Arrange bread pieces on prepared tray. Sprinkle with cinnamon sugar. Bake, turning bread halfway through, for 15 minutes or until golden.
Meanwhile, using an electric mixer, beat the remaining cream until just-firm peaks form. Fold into cooled mousse mixture, being careful not to over-mix as the mousse will start to split.
Spoon mousse, marshmallow cream and 3/4 of the hot fudge sauce, alternating and slightly marbling, into cob. Top with mini marshmallows and remaining fudge sauce. Sprinkle with grated chocolate and serve with toasted bread pieces, wafers, pretzels, wafer sticks and extra mini marshmallows.