01 -  Preheat the oven to 325°F. Line each cavity of a 12-cup muffin tin with paper liners. 
 02 -  Stir together graham cracker crumbs, granulated sugar, and melted butter until the mixture is evenly moistened. Distribute about 1 tablespoon into each muffin liner and press firmly to form an even layer. Bake for 5 minutes, then remove from the oven and allow to cool slightly. 
 03 -  Using an electric mixer, beat cream cheese and sugar until completely smooth. Blend in the egg, sour cream, and vanilla extract just until combined. Gently fold in the cooled, melted semi-sweet chocolate. 
 04 -  Evenly spoon the cheesecake filling onto each crust, smoothing the tops. Bake for 18 to 20 minutes or until centers are just set. Remove from the oven and cool to room temperature. 
 05 -  Transfer cooled cups to the refrigerator and chill for at least 2 hours to set. 
 06 -  Place one marshmallow on each chilled cheesecake cup. Toast for 1 to 2 minutes under a broiler on high, or use a kitchen torch until marshmallows are browned and slightly blistered. 
 07 -  Drizzle with melted milk chocolate and sprinkle with extra graham cracker crumbs if desired. Serve immediately while marshmallows are warm.