Grease a 9x13 inch pan. In a bowl, melt the butter, peanut butter, and the butterscotch chips in the microwave, stiring occasionally until smooth.
Let stand to cool until the mixture is warm to the touch (if you can leave your finger in it comfortably for 5 seconds, then it is ready). Add marshmallows. Fold until all the marshmallows are covered.
Put in baking dish. Chill in fridge for about 2 hours(or until hardened). Serve and enjoy!