Spray a 9x13-inch pan with non-stick spray or line with waxed paper or parchment paper.
To a large, deep saucpan over medium-low heat, add butter, peanut butter, and butterscotch chips. Stir frequently until the mixture is completely melted and smooth.
Remove from the heat and fold in peanuts, cereal, and marshmallows. Gently fold until everything is evenly coated.
Pour the mixture into your prepared pan spread to evenly.
Cool completely before cutting. You can put the pan in the refrigerate to speed the cooling process. Don't cover until the bars are cooled completely. Cut into bars.
Store either on the counter or in the refrigerator in an airtight container.