Preheat your oven to 350°F (175°C). Combine the graham cracker crumbs and melted unsalted butter in a mixing bowl until evenly mixed. Press into the bottom of the baking dish to form a solid crust. Bake for 10 minutes until lightly golden and let cool completely.

Prepare the chocolate cake mix in a separate bowl according to package instructions. Pour the batter over the cooled graham cracker crust. Bake for 30-35 minutes until a toothpick comes out clean. Cool for 10-15 minutes.

Use a wooden spoon or skewer to poke holes all over the cake surface, about an inch apart, to allow filling to seep in.

Whisk together the chocolate pudding mix with the recommended amount of milk until thickened, about 2-3 minutes. Pour it evenly over the cake, filling all the holes. Let it set for 5-10 minutes.

Spread a layer of marshmallow fluff over the pudding layer, then dollop whipped cream on top, smoothing it out to maintain airiness.

Scatter mini marshmallows and graham cracker chunks over the whipped cream layer. Broil for 30 seconds until lightly toasted, watching closely to prevent burning.

Let the cake set in the refrigerator for at least 1 hour before serving, then slice and enjoy chilled or slightly warm.