Whisk together the sweetened condensed milk and peanut butter in a large bowl. Set aside.
Use a stand or hand mixer to whip the heavy whipping cream into heavy peaks. Gently fold the whipping cream into the sweetened condensed milk mixture until combined.
Stir in the peanut butter cups. Be sure to use the miniature peanut butter cups, not the peanut butter cup minis (which are the already unwrapped, much smaller, peanut butter cups).
Pour ice cream batter into a freezer safe container and cover.
Freeze for at least 6 hours, preferably overnight, before serving.