Line an 8x8-inch baking dish with foil.

In a large microwave safe bowl, combine the butterscotch chips, peanut butter and butter. Microwave on 50% power in 30 second intervals until melted, stirring after each interval. Stir until smooth.

Stir in the vanilla, salt, 2 cups of the marshmallows and 1/2 cup of the peanuts. Pour the mixture into the prepared pan. Sprinkle the remaining marshmallows and peanuts on top and press lightly into the top with your hands. Chill until set, 15 minutes in the freezer or an hour in the fridge.

Cut into 25 squares.