Line a 9 x 9 pan with parchment paper and lightly spray with cooking spray.
Evenly space 16 peanut butter cups in the pan.
Melt chocolate chips and condensed milk in microwave by heating for 1 minute then stirring and repeating (probably 3-5 minutes depending on your microwave).
Spread melted chocolate over peanut butter cups in pan.
Cut or break up remaining 4 peanut butter cups and sprinkle evenly over pan, pressing lightly into the fudge.
Refrigerate to set, then cut into squares.