1-1/2 teaspoons plus 1/2 cup butter, softened, divided
2 cups packed brown sugar
1 cup sugar
1 cup evaporated milk
1 jar (7 ounces) marshmallow creme
1/3 cup peanut butter
1 teaspoon vanilla extract
1 cup butterscotch chips
Line a 9-in. square pan with foil and grease the foil with 1-1/2 teaspoons butter; set aside. In a large heavy saucepan, combine the sugars, milk and remaining butter. Cook and stir over medium heat until sugar is dissolved. Bring to a rapid boil; boil for 5 minutes, stirring constantly. Reduce heat to low; stir in the marshmallow creme and peanut butter until melted and blended.
Remove from the heat; stir in vanilla. Add the butterscotch chips; stir until chips are melted. Pour into prepared pan. Refrigerate for 4 hours or until firm. Using foil, remove fudge from pan; carefully peel off foil. Store in refrigerator.