Preheat your oven to 350°F (175°C). In a 9×13 inch pan, prepare the chocolate cake mix according to package instructions, mixing until smooth. Pour the batter into the prepared pan and bake for around 30–35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool slightly before moving to the next step.

While the cake is still warm, use the handle of a wooden spoon to poke holes evenly across the surface, about 1-inch apart.

In a microwave-safe bowl, combine the sweetened condensed milk, semi-sweet chocolate chips, and heavy cream. Heat the mixture in the microwave on high for about 1 minute, then stir until smooth. Pour this ganache generously over the cake.

Allow the cake to cool at room temperature for about 1 hour. Optionally, refrigerate for an additional 30 minutes.

In a mixing bowl, pour cold heavy cream and add powdered sugar. Whip until stiff peaks form, then gently fold in the marshmallow fluff. Spread this mixture over your chilled cake.

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

Slice into generous pieces and serve. Enjoy the luxurious dessert experience!