In a saucepan over medium heat combine butter, peanut butter and butterscotch chips stirring frequently. Alternatively combine in a bowl and microwave in 30 second increments, reducing to 15 second increments until melted and combined stirring between.
Allow to cool 5 minutes.
Fold in miniature marshmallows and pour into lined pan.
Refrigerate 1+ hours before cutting into squares and serving.
Notes
Tips
Add in peanuts or candy coated chocolates like M&M's, Peanut Butter M&M's, or Reese's Pieces.
Use creamy peanut butter (avoid natural as sometimes the oils don't blend well).
Don't add the marshmallows to the bars right after the liquid mixture comes off the stove - you'll risk melting the marshmallows. Let it cool just a bit before adding them.