For the crust:
1 cup graham cracker crumbs
1 tbsp. sugar
4 tbsp. unsalted butter, melted
For the cheesecake:
4 oz. bittersweet or semisweet chocolate, finely chopped
8 oz. cream cheese, at room temperature
¼ cup sour cream
½ cup marshmallow cream
2 tsp. cocoa powder
¾ tsp. vanilla extract
2 large eggs
For the topping:
1½ cups mini marshmallows
Milk chocolate chips, melted (optional)
To make the crust, preheat the oven to 350˚ F. Line an 8×8″ baking pan with foil; spray lightly with cooking spray. Combine the graham cracker crumbs, sugar and melted butter in a small bowl. Stir together with a fork until well combined. Press the mixture in an even layer into the bottom of the prepared baking pan. Bake 10 minutes; transfer to a wire rack while you prepare the filling. Reduce the oven temperature to 325˚ F.
To make the filling, place the chopped chocolate in a heatproof bowl set over a pan of simmering water. Heat until melted and smooth, stirring occasionally. Remove from the heat and let cool slightly. In the bowl of a stand mixer fitted with the paddle attachment, combine the cream cheese, sour cream and marshmallow cream. Beat on medium-high speed until smooth and well combined, 1-2 minutes. Blend in the cocoa powder, vanilla extract and eggs until incorporated. Stir in the melted chocolate until well blended. Pour the filling over the graham cracker crust and smooth the top with a spatula. Bake about 30 minutes, or until the center is just set (does not jiggle when shaken gently.) Remove from the oven.
Evenly top the cheesecake layer with the mini marshmallows. Return to the oven for 2-3 minutes, just long enough so the marshmallows begin to melt into each other. Transfer to a wire cooling rack. Using a kitchen torch, lightly brown the tops of the marshmallows. (Alternatively, this can be done underneath the broiler with a very watchful eye.) Once the cheesecake has cooled to room temperature, drizzle with melted milk chocolate if desired. Transfer to the refrigerator and chill 2-3 hours before slicing and serving.