Preheat your oven to 350 degrees F and spray a 24-cup mini muffin tin with non-stick cooking spray.
Grab your peanut butter cookie dough and slice it into 24 equal squares (just follow the perforated lines), then drop one square of cookie dough into each mini muffin tin cavity.
Bake for 12-15 minutes, then immediately take the handle of a spoon or spatula and press down in the center of each cookie to create a well and set aside to cool.
In a medium mixing bowl, combine peanut butter, butter, powdered sugar, heavy whipping cream, and vanilla extract, then mix until smooth and creamy.
Transfer the peanut butter filling into a piping bag or Ziploc bag, cut off one end, and fill each cookie cup about halfway full.
Transfer the marshmallow fluff into a piping bag or Ziploc bag, cut off one end, and fill the remaining space of each cookie cup.
Top the cookie cups with chopped peanuts before enjoying!