In a large pot over medium-low heat, combine the butter, peanut butter, and butterscotch chips. Stir frequently until the mixture is completely melted.
1/2 cup (113g) unsalted butter, 1 cup (270g) creamy peanut butter, 11 oz butterscotch chips
Remove from the heat and stir in coconut, walnuts, and marshmallows. Pour the mixture into an ungreased 9x13 inch pan and spread to even it out. Allow the mixture to set, then cut into bars. To speed up the process of setting, place in a cold garage or refrigerator.
1 cup (85g) sweetened flaked coconut, 1 cup chopped walnuts, 10 oz mini marshmallows
OR use a cookie scoop to portion out into mini muffin cups.