Line a 13-in. x 9-in. pan with foil and grease the foil with 1-1/2 teaspoons butter; set aside.
Microwave the chocolate chips, butterscotch chips and peanut butter at 70% power for 2 minutes; stir. Microwave in 10- to 20-second intervals until melted; stir until smooth. Cool for 1 minute. Stir in marshmallows and peanuts.
Spread into prepared pan. Refrigerate until firm. Using foil, lift candy out of pan. Discard foil; cut into 1-1/2-in. squares.