Melt butter in a saucepan, add peanut butter and butterscotch chips and melt together.
Now comes the hard part - LEAVE IT TO COOL. At least 15 minutes! Until the bottom of the pan is cool!
Once cooled, pour over marshmallows.
Once everything is coated and mixed, transfer it to a greased 8x8 or 9x9 baking dish and refrigerate.
Cut into small squares and put in freezer to keep.
Notes
For Rocky Road Bars: Substitute chocolate chips for the butterscotch chips. When adding cooled mix to the marshmallows, I added crushed pecans (about 300gm or so).