Preheat your oven to 325°F (163°C) and prepare a water bath by placing a large baking dish filled with hot water on the bottom rack of your oven.

In a mixing bowl, combine chocolate cookie crumbs with melted unsalted butter until it resembles wet sand. Firmly press into the bottom of a 9-inch springform pan and bake for 10 minutes. Set aside to cool.

Beat softened cream cheese with granulated sugar until smooth and creamy. Gradually add eggs, mixing well after each addition, then blend in hot cocoa mix until fully incorporated.

Pour the cheesecake filling over the cooled crust and bake in the water bath for 50 to 60 minutes until the edges are set and the middle is slightly jiggly.

Turn off the oven and leave the cheesecake inside for an additional hour to cool gradually, then transfer to the refrigerator to chill for at least 4 hours or overnight.

Whip heavy cream on high speed until soft peaks form, then fold in marshmallow fluff to create a light, fluffy topping.

Spread the marshmallow whipped cream over the chilled cheesecake and garnish with mini marshmallows or chocolate shavings if desired.

Slice and serve your Hot Cocoa Cheesecake chilled, ideally paired with a warm cup of cocoa.