Line an 8-in. square pan with foil; grease with butter., In a heavy saucepan, combine sugar and milk; bring to a boil over medium heat, stirring constantly. Boil 3 minutes, stirring constantly. Remove from heat., Stir in peanut butter and marshmallow creme until blended. Immediately spread into prepared pan; cool slightly., Refrigerate until firm. Using foil, lift fudge out of pan. Remove foil; cut into squares. Store between layers of waxed paper in an airtight container.