Adjust the oven rack to the lower-middle position. And preheat the oven to 325°F (160°C), or 140°C if using a fan oven.
Lightly grease a 9-inch (23 cm) springform pan with butter, then line it with parchment paper (bottom and sides).
Place the oreo cookies in a large food processor and blend on high until just crumbs remain. Add the butter and pulse to mix. Mixture should resemble wet sand.
Press the mixture into the bottom and halfway up the sides of the prepared pan. Bake in the preheated oven for 10-12 minutes, or until the crust looks dry. Allow to cool on a wire rack.
In a large bowl, beat the cream cheese, granulated sugar, and smooth peanut butter on high speed until smooth and creamy. Add the eggs, one a time, mixing well and scraping the sides of the bowl after each.
Add the sour cream, heavy cream, and vanilla and mix well. Fold in the reeses cups.
Pour the peanut butter cheesecake batter into the prepared crust. Wrap the bottom and sides of the springform pan with foil.
Prepare a water bath by placing a roasting pan in the oven and then placing the cheesecake pan (that you've wrapped in foil) in the middle of it. Pour boiling water around the cheesecake until it's an inch deep.
Bake in the preheated oven for 40-50 minutes, or until the cheesecake center is set but still wobbly. Turn the oven off, open the door, and allow the cheesecake to cool for one hour. Remove from the oven and place into the fridge to chill for at least 4 hours.
Once the cheesecake has been chilled, prepare the ganache by heating the heavy cream until it is steaming (do not boil).
Pour the cream over the chocolate chips in a large heatproof bowl and allow to sit for 5 minutes. Stir until no lumps remain. Pour the ganache over the cheesecake and use the back of a spoon or an offset spatula to spread it evenly over the surface of the cheesecake.
Decorate the edges of the cheesecake with chopped peanut butter cups. Serve with a generous drizzle of caramel sauce.