Butterscotch Sauce

In a medium saucepan combine butter, half-and-half, light-color corn syrup and brown sugar. Cook and stir over medium-high heat until mixture boils. Reduce heat; boil gently for 3 minutes more, stirring frequently. Stir in vanilla. Serve warm (mixture may need to be lightly stirred or whisked again before serving). Chill leftovers, covered, for up to 3 days. Reheat before serving*.