Preheat your oven to 350°F (175°C). In a large mixing bowl, combine the chocolate cake mix, eggs, water, and oil as per package instructions. Pour the batter into a greased 9x13 inch baking dish, then bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Allow the cake to cool in the pan for about 15 minutes before moving it to a wire rack to cool completely.

Once the cake has cooled, take the handle of a wooden spoon and gently poke holes about 1 inch apart across the surface of the cake, being careful not to poke all the way through to the bottom.

In a microwave-safe bowl, add 2 cups of marshmallow fluff along with 2 tablespoons of water. Microwave the mixture for about 30 seconds, stirring until you achieve a smooth pouring consistency. Carefully pour or pipe the marshmallow fluff into the holes you created in the cake.

For the chocolate fudge topping, in a medium microwave-safe bowl, combine 1 cup of chocolate chips, 1 can of sweetened condensed milk, and 2 tablespoons of heavy cream. Microwave in 30-second intervals, stirring until smooth and creamy. Spread the fudge mixture over the top of your filled Hot Chocolate Poke Cake.

Place the cake in the refrigerator and chill for at least 1 hour, or until the chocolate fudge topping has set completely.

In a clean mixing bowl, pour in 1 cup of heavy whipping cream. Add 2 tablespoons of instant hot chocolate mix and a splash of vanilla extract. Using an electric mixer, whip the cream on medium-high speed until stiff peaks form, about 3-5 minutes. Spread the whipped cream over the chilled cake.

Top your Hot Chocolate Poke Cake with a generous sprinkle of mini marshmallows and drizzle warm hot fudge sauce over the top if desired. Serve slices chilled or at room temperature.