Preheat oven to 350°F. Line a 12-cup muffin pan with liners.
Place graham crackers in a large ziploc bag. Seal the bag except for 1” and roll with a rolling pin to crush the graham crackers to a fine crumb. This can also be done in a food processor. Stir graham cracker crumbs with sugar and melted butter. Scoop 1-2 tablespoons of the crust mixture into the bottom of each muffin cup (for a total of 12). Press to compact.
Beat cream cheese until smooth, about 30 seconds, using a stand mixer fitted with the paddle attachment or a hand mixer. Beat in sour cream, egg, sugar, and vanilla. Beat until no lumps remain. (It’s helpful if all ingredients are room temperature before starting!)
Melt semi-sweet baking chocolate in a small bowl on high power in 30 second increments, stirring between each, until melted and smooth. Place 1/4 cup of the cheesecake batter into the chocolate mixture and stir to combine.
Divide the remaining plain cheesecake batter evenly on top of the crusts (about 1 tablespoon per muffin cup). Scoop about 1 teaspoon of the chocolate cheesecake batter on the top and swirl with a toothpick to create the marbled look.
Bake cheesecakes for about 18-21 minutes until the tops are puffed and slightly cracking. Cool completely, then chill for at least 2 hours or overnight.
To serve: remove the cupcake liner and top with chocolate whipped cream and PEEPS® Marshmallow Snowmen or PEEPS® Marshmallow Trees!