First, preheat your oven to 325°F (160°C). Wrap the outside of a 9-inch springform pan with aluminum foil to prepare for the water bath. This will prevent water from seeping into the pan. Meanwhile, boil 3 cups of water.
In a medium bowl, combine the crushed Oreo cookies and melted butter. Stir until the crumbs are evenly coated. Press the mixture into the bottom of the prepared springform pan to create an even crust. Place it in the refrigerator to chill while you prepare the filling.
In a large mixing bowl, beat the softened cream cheese, peanut butter, and sugar until smooth and creamy. Add the eggs, one at a time, mixing well after each addition. Finally, stir in the vanilla extract.
Take the crust out of the refrigerator and pour the cheesecake filling over it. Smooth the top with a spatula.
Prepare a large roasting pan and place the springform pan in the center. Fill the roasting pan with enough of the hot water to reach about halfway up the sides of the springform pan. This creates a water bath and helps ensure even baking and a creamy texture for the cheesecake.
Carefully transfer the roasting pan with the cheesecake to the preheated oven. Bake for about 1 hour or until the edges are set, but the center still jiggles slightly when gently shaken. Turn off the oven and leave the cheesecake in the oven with the door slightly ajar for about 1 hour.
Remove the springform pan from the water bath and let the cheesecake cool completely on a wire rack. Once cooled, refrigerate for at least 4 hours or overnight to allow it to set.
Just before serving, prepare the chocolate ganache. In a small saucepan, heat the heavy cream over medium heat until it starts to simmer. Remove from heat and add the chocolate chips. Let it sit for a minute, then whisk until smooth and shiny.
Take the chilled cheesecake out of the refrigerator and carefully remove the sides of the springform pan. Pour the chocolate ganache over the top of the cheesecake, allowing it to drip down the sides.
Return the cheesecake to the refrigerator for another 30 minutes to allow the ganache to set.
Once the ganache is set, slice the cheesecake and serve. Top with chopped Reese’s cups if desired!