01 - Preheat the oven to 325°F. Line a 12-cup muffin tin with paper liners.
02 - Combine graham cracker crumbs, granulated sugar, and melted butter in a bowl until evenly moistened. Press approximately 1 tablespoon of crust mixture into the bottom of each liner. Bake for 5 minutes, then remove from the oven and set aside.
03 - In a mixing bowl, beat cream cheese with granulated sugar until smooth and creamy. Incorporate the egg, sour cream, and vanilla extract, mixing just until combined. Fold in melted and cooled semi-sweet chocolate chips.
04 - Divide the cheesecake filling evenly among the prepared crusts. Gently smooth the tops.
05 - Bake for 18 to 20 minutes, or until the centers are just set. Allow to cool at room temperature, then refrigerate for at least 2 hours until fully chilled.
06 - Place a large marshmallow atop each cheesecake cup. Broil on high for 1 to 2 minutes or use a kitchen torch to toast until golden brown.
07 - Optionally, drizzle with melted milk chocolate and sprinkle with extra crushed graham crackers prior to serving.