1-Bake the cake in a 9 x: Bake the cake in a 9 x 13-inch dish according to the directions listed on the box.
2-When the cake is baked, using the: When the cake is baked, using the handle of a wooden spoon poke the cake, making the holes about an inch apart. Do not poke it all the way to the bottom just about 2/3 of the height.
3-Place 2 cups of marshmallow fluff in: Place 2 cups of marshmallow fluff in a microwave-safe bowl and add 2 Tablespoons water. Microwave in a 20-second interval and stir until smooth. You can pour it from a jug or place it in a zip-lock bag, cut off the corner, and then pipe it into the holes. Spread the remaining on top. Place the cake in the fridge.
4-Next, place chocolate chips sweetened condensed milk,: Next, place chocolate chips sweetened condensed milk, and 2 Tablespoons of heavy cream in a microwave-safe bowl and heat in 20-second intervals, stirring until smooth. Spread over the cake and chill until the chocolate is cooled completely.
5-Beat 2 cups of heavy whipping cream: Beat 2 cups of heavy whipping cream with vanilla and instant hot chocolate mix until stiff peaks form. Spread over the chilled cake and garnish with mini marshmallows.
6-Drizzle with chocolate fudge sauce before serving,: Drizzle with chocolate fudge sauce before serving, if desired.