In a medium bowl, whisk together the finely-crumbled Oreo cookies and melted butter until blended. Press the mixture into your mini cheesecake pan (or other baking pan) in your desired thickness, press until flat, then bake for 5 minutes and remove.
To Make The Peanut Butter Cheesecake:
In an electric mixer, add the cream cheese and peanut butter and beat on medium-speed until smooth. Add the sugar and continue mixing until combined. Blend in the eggs one at a time, then the cream and vanilla, using a spatula to scrape down the bowl between additions, and beat until just combined.
Use a spoon or cookie scoop to transfer the batter to your pan with the pre-baked crusts. Fill each mini cheesecake container to the brim, evening out the tops with a spoon. Then bake for 12-15 minutes, or until the cheesecakes are just set and no longer move when you jiggle the pan. Turn the oven off and crack open the door and let the cheesecakes cool off for 15 minutes. Remove and let sit until they reach room temperature, then refrigerate for at least 4 hours. Top with ganache and the crumbled Reese's.
To Make The Chocolate Ganache:
In a heatproof bowl, add the chocolate chips and cream. Heat over a bowl of simmering water, stirring until combined and the chocolate is melted. Or heat in the microwave in 10-second intervals, stirring between intervals, until the chocolate is melted. Add in a tablespoon of powdered sugar, or more to reach your desired consistency. Then spoon the ganache over the mini cheesecakes.