Pulse Oreo cookies in the work bowl of a food processor until they are fine crumbs. Transfer to a medium bowl, add the melted butter and mash together with a fork or spoon until well combined. Press mixture into the bottom and sides of a 9” springform pan or deep dish pie plate. Transfer to the fridge for at least 30 minutes to chill. You can also bake it at 350℉ for 8-10 minutes, then chill for a more stable crust.
Finely chop 9 of the Reese’s peanut butter cups, set aside.
To prepare the filling, beat the cream cheese, cold, for a full minute with hand mixer or in a stand mixer on medium high.
Add sugar and beat until sugar is melted and no longer grainy, about 2-3 minutes. Add cocoa, milk, and vanilla. Beat until well combined and creamy. Gently fold in the whipped topping.
Fold about 2/3 of the chopped Reese's peanut butter cups into the chocolate mixture. Pour half of the mixture into the prepared Oreo crust, smoothing the top with the back of a spoon or silicone spatula. Place about 7 Reese's peanut butter cups through the pie. Top with remaining mixture and gently smooth with the back of a metal spoon.
Sprinkle remaining chopped Reese's on top for garnish.
Refrigerate for at least 3 hours before serving. Garnish with any additional optional garnishes just before serving. This cheesecake is also delicious frozen. Just set out for 20 minutes before slicing.