Beat peanut butter, sour cream, mayonnaise and vanilla together well. Gradually add the powdered sugar.
Once blended, fold in 3/4 tub cool whip and reserve the rest for topping. Or you can fold in the entire tub - your choice.
Pour onto cooled brownie layer and refrigerate or freeze until ready to serve. (Refrigerate for at least 2 hours or freeze for 1 hour before serving)
Garnish with Chocolate sauce, crushed peanuts and reserved cool whip to your liking.