Preheat your oven to 350 degrees F.
Spread the melted peanut butter evenly on the bottom of an 8-inch cast-iron skillet.
Arrange the peanut butter cups on top, followed by a layer of marshmallows. Stick the chocolate squares upright between the marshmallows.
Bake for 8-10 minutes or until the marshmallows turn golden.
Serve it warm with cookies, graham crackers, or anything else you like!