Preheat your oven to 350°F (175°C). In a mixing bowl, crush graham crackers until fine crumbs form, then combine with melted unsalted butter. Press into the bottom of a greased springform pan. Bake for 10 minutes, then cool.

In a large mixing bowl, beat together cream cheese, sour cream, and heavy cream until smooth. Fold in chopped marshmallows. Pour the filling over the cooled crust.

Bake for 45 to 60 minutes until edges are set but center jiggles slightly. Turn off oven and leave cheesecake inside for 30 minutes to cool gradually.

Cool cheesecake at room temperature for about an hour, then refrigerate for at least 4 hours, or overnight.

For the ganache, bring heavy cream to a gentle simmer. Pour over chopped semi-sweet chocolate and stir until combined. Cool slightly.

Once cheesecake is cooled, pour ganache over the top, spreading it evenly.

Arrange marshmallows on top of the ganache. Use a kitchen torch or broiler on low to toast marshmallows until golden brown.

Slice and serve the cheesecake with whipped cream or vanilla ice cream.