Peanut Butter Marshmallow Squares

In the lower pot of a double boiler, add water halfway to top and bring to a boil. Reduce heat to a simmer. In the top of a double boiler, heat butter, butterscotch chips, and peanut butter until melted. Remove from heat.
Stir in coconut, walnuts, and marshmallows.
Pour mixture in buttered pan. Refrigerate and cut into squares. Store in the refrigerator.