In a medium bowl stir together oreo crumbs and melted butter.. Press into the bottom of a 9-inch springform pan. Place springform pan on a baking sheet and place in oven for 8 minutes. Set aside.
To make filling, place chocolate chips in a microwave-safe bowl and microwave on HIGH at 20 second intervals until smooth when stirred. Set aside.
Using an electric mixer, beat cream cheese at medium speed until smooth.
Add sweetened condensed milk and vanilla and beat on LOW until combined.
Beat in eggs, one at a time, beating just until combined.
Beat in melted chocolate just until combined.
Place peanut butter cups on top of cooled oreo crust.
Pour batter over peanut butter cups.
Place in 300 degree oven for 1 hour 5 minutes. Turn oven off and leave cheesecake in oven with door closed for 1 hour.
Remove cheesecake from oven, run a knife around the edge. Let cool to room temperature and then remove sides of pan. Make ganache and pour on top of cheesecake.
To make ganache, bring whipping cream to a simmer in a small saucepan. Stir in chocolate chips and remove from heat. Continue to stir until smooth. Let cool slightly before pouring on cheesecake. Refrigerate cheesecake at least 8 hours.
To make peanut butter frosting, beat cream cheese with electric mixer. Add peanut butter and beat until evenly combined.
Beat in powdered sugar and enough milk to make it thin enough to pipe.
Place icing in a pastry bag fitted with a large star tip and swirl around the edges.