Mix together the melted butter and granola. Press the mixture into an 8" cheesecake pan or 4 mini pans. Allow to refrigerate while you prepare the filling.
Melt the chocolate with a double boiler, or in the microwave.
Add the melted chocolate, cream cheese, sour cream, powdered sugar, and vanilla to a bowl. Mix on high until smooth and creamy.
Pour the cheesecake filling over the chilled crust and smooth it out. Allow it to chill in the refrigerator for at least 4 hours.
Spread the marshmallow fluff over the top of the cheesecake. Use a kitchen torch to toast it if desired.