Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.
In a small bowl, combine crushed cookies and melted butter. Press about 1 tablespoon of the mixture into the bottom of each muffin liner.
In a large bowl, beat cream cheese and sugar until smooth. Beat in eggs one at a time, then stir in sour cream, vanilla extract, and peanut butter until well combined.
Spoon the filling evenly into the prepared muffin liners over the crust.
Bake for 20-25 minutes, or until the edges are set and the centers are slightly jiggly.
Let cool in the muffin tin for 10 minutes, then transfer to a wire rack to cool completely.
While cheesecakes are cooling, prepare the chocolate ganache. In a small microwave-safe bowl, combine chocolate chips and heavy cream. Microwave on high in 30-second intervals, stirring in between, until smooth.
Once cheesecakes are completely cooled, top each with a halved Reese's Peanut Butter Cup and drizzle with chocolate ganache.
Chill for at least 1 hour before serving.
Notes
These mini cheesecakes are best served chilled. You can make them ahead of time and store them in the refrigerator.