Line an 8×8 inch baking pan with aluminum foil and lightly spray with cooking spray.
Chop the mini Reese’s into quarters and the regular size Reese’s into eights. Reserve the regular size Reese’s for the topping and then place the chopped mini cups in the bottom of the pan.
In a large glass bowl, stir the chocolate chips and sweetened condensed milk together. Cook in the microwave on 50% power in 30 second intervals, stirring after each time.
Once chocolate is melted, spread evenly over the peanut butter cups.
Sprinkle reserved chopped Reese’s on top and gently press into chocolate.