Preheat your oven to 350°F (175°C). In a large mixing bowl, prepare the Devil's Food Chocolate Cake mix according to the package instructions. Pour the batter into a greased 9x13 inch baking pan. Bake for about 30-35 minutes, or until a toothpick inserted in the center comes out clean. Once done, let the cake cool for about 10 minutes before proceeding.

After cooling, use the handle of a wooden spoon or a similar tool to gently poke holes all over the surface of the warm chocolate cake, about 20 holes evenly spaced.

In a microwave-safe bowl, combine the sweetened condensed milk, semi-sweet chocolate chips, and heavy cream. Microwave in 30-second intervals, stirring until smooth. Pour the warm ganache evenly over the holes in the cake.

Place the cake in the refrigerator to chill for at least 2 hours or until the ganache is set.

In a mixing bowl, whip the heavy cream and powdered sugar together using an electric mixer on high speed until stiff peaks form, taking about 3-5 minutes. Gently fold in the marshmallow fluff.

Spread the whipped marshmallow topping over the cooled cake, creating a smooth layer.

Melt additional chocolate chips with a splash of heavy cream in the microwave until smooth. Drizzle this mixture over the marshmallow topping.

Slice your cake into squares and serve it chilled. Enjoy!