First, preheat your oven to 325°F (165°C). Place the whole Oreos in a food processor and pulse until they become fine crumbs. Pour in the melted butter and mix until the crumbs are evenly moistened, resembling wet sand. Press this mixture firmly into the bottom and up the sides of your 9-inch pie dish. Bake for 15 minutes, then let it cool completely.
In a medium bowl, beat the room temperature cream cheese until it's completely smooth. Add the cocoa powder, sugar, sour cream, and vanilla extract, mixing until well combined. Gently stir in the melted dark chocolate until the mixture is uniform and glossy. Pour this decadent chocolate layer evenly over your cooled Oreo crust and set it aside.
In a large bowl using a mixer, beat the cream cheese and sugar until fluffy. Add the creamy peanut butter, vanilla extract, and sour cream, mixing until smooth. In a separate bowl, whip the cold heavy cream with powdered sugar until stiff peaks form. Gently fold the whipped cream into the peanut butter mixture until no streaks remain, creating a light and airy mousse.
Carefully spoon the peanut butter mousse on top of the chocolate layer, spreading it into an even layer. For a final touch, drizzle melted peanut butter over the top and sprinkle with chopped peanut butter cups. Cover the pie and refrigerate for at least 3 hours, or preferably overnight, to allow it to set completely before slicing and serving.