Lightly grease a 13- by 9- inch pan with nonstick spray. Crush Oreos in a blender then transfer to a medium bowl. Mix in the melted butter and toss to coat. Evenly press into the bottom of the pan.
In a medium bowl, combine the peanut butter, powdered sugar and cream cheese until smooth. I use my stand mixer fitted with the paddle attachment, but you can also use a wooden spoon or rubber spatula. Fold in half of the Cool Whip, then spread over the Oreo crust.
In another medium bowl, whisk the chocolate pudding mix into the 2 cups of milk. Let stand for 2 minutes to thicken, then evenly spread over the peanut butter cream cheese layer.
Spread the remaining Cool Whip over top then sprinkle with the chopped Butterfinger candy bars. Cover with plastic wrap and refrigerate for at least 1 hour before serving. Keeps in the fridge for a few days, but no longer than 1 week.