Grease a 9×13 inch baking pan with cooking spray. I also lined mine with parchment paper so it would be easier to remove (and clean the pan!).
Spread 1 ½ cups of peanuts on the bottom of the pan. Set aside.
In a medium sized bowl, add peanut butter chips and butter. Heat in the microwave for 1 minute at medium power. Stir. Heat again on medium power for another 20 seconds. Stir. Continue to reheat at these intervals until mixture is melted. Be careful to not burn it though! Mine melted after I stirred it together.
Pour in the sweetened condensed milk and stir to combine. Heat in the microwave for 1 minute on high.
Stir in Marshmallow Fluff and Snickers bars.
Pour mixture into baking pan. Sprinkle with the remaining 1 ½ cups peanuts.
Refrigerate for 3 hours or until set. Cut into squares.