While brownies are baking or cooling...you can make the peanut butter fluff ahead of time.
Using mixer, whip whipping cream until it starts getting fluffy.
Add in peanut butter, powdered sugar and vanilla until continue whipping until peaks become stiff, keep in fridge until layering.
Sprinkle an even layer of nutter butter cookie bits on top of brownies.
Pour and spread the peanut butter fluff on top of of the cookie / brownie layer.
Cover and put in fridge.
Melt chocolate chips and add in cream after melted and whisk If it's too thick, add in a little more cream. It should be thick and creamy. Drizzle with piping bag or snip hole in ziplock bag and fill with chocolate and drizzle on top of fluff.
Pop peanut butter in microwave about 15 seconds and do the same drizzle method like the chocolate.
Sprinkle some random mini Reese's Pieces and transfer to the refrigerator overnight.
Keep refrigerated or frozen until use.