Preheat oven to 325 degrees Fahrenheit and grease a 9-inch springform pan.

Mix graham cracker crumbs, 1/4 cup cocoa powder, and melted butter in a bowl until combined.

Press the mixture firmly into the bottom of the prepared springform pan and bake for 8 minutes, then set aside to cool.

In a large bowl, beat softened cream cheese and sugar until smooth and creamy.

Sift in the Dutch-process cocoa powder and mix until incorporated.

Stir in the sour cream, heavy cream, and vanilla extract.

Add eggs one at a time, beating on low speed until just combined to avoid incorporating excess air.

Pour the cheesecake batter over the prepared crust.

Bake for 65 to 75 minutes until the edges are set but the center remains slightly jiggly.

Turn off the oven and leave the cheesecake inside with the door slightly ajar for 1 hour.

Refrigerate the cheesecake for at least 6 hours or overnight.

Heat 1/4 cup heavy cream and pour over chocolate chips, stirring until smooth to create ganache.

Spread ganache over the chilled cheesecake and top with mini marshmallows.

Toast marshmallows using a kitchen torch or briefly under a broiler until golden brown.