Preheat your oven to 350°F (175°C). Crush the Oreo cookies into fine crumbs and combine with melted unsalted butter. Press into a 9-inch springform pan and bake for 10 minutes.

In a large bowl, beat the cream cheese and granulated sugar until smooth. Gradually add the hot cocoa mix, sour cream, vanilla extract, and heavy cream, mixing until fully incorporated.

Add the eggs one at a time, mixing on low speed just until blended. The mixture should be smooth and homogenous.

Pour the filling over the cooled crust and spread evenly. Bake in a water bath for 60–75 minutes until edges are set but the center jiggles.

Turn off the oven and let the cheesecake cool inside for 1 hour with the door slightly ajar. Then, refrigerate overnight.

When ready to serve, top with whipped cream and cocoa powder, and add mini marshmallows for garnish.