In a 1-1/2-qt. microwave-safe dish, combine the brown sugar, corn syrup, butter and salt. Cover and microwave on high for 2-1/2 minutes or until mixture boils, stirring twice. Add peanut butter; stir until smooth. Stir in evaporated milk.
Serve warm over ice cream. Sprinkle with peanuts if desired. Cover and store in the refrigerator. To reheat, microwave at 50% power for 30-60 minutes or until heated through.