Line a 9x9? pan with foil and spray with cooking spray. Place the peanut butter cups in an even layer on the bottom of the pan. (You should use 16 on the bottom)
Place chocolate chips and sweetened condensed milk in a medium saucepan over low heat. Stir until chips and milk are melted together.
Once everything is melted together, spread evenly over peanut butter cups in prepared pan. Immediately sprinkle with the crumbled Reese's, pressing them lightly into the fudge. Cool until firm. I like to cool the fudge on the counter until it?s room temperature, then cover with plastic and place in the refrigerator to harden completely. Cut into squares and serve.