Using a food processor, blend Oreo cookies, peanuts, and melted butter until fine crumbs. Press the mixture into the bottom of a 10-12 inch tart pan. Refrigerate while preparing the filling.
In a large mixing bowl, combine cream cheese, peanut butter, powdered sugar, and milk. Blend until smooth. Add half of the whipped topping (8 ounces) and mix until combined. Fold in chopped peanut butter cups.
In another bowl, mix chocolate pudding mix and cold milk until well combined. Set aside until it thickens.