In a 3- to 4-quart pan over high heat, stir butter or margarine and sugar until mixture is caramel-colored, 2 to 4 minutes. Remove from heat and add whipping cream; stir until blended (mixture foams). Return to high heat and stir until caramel sauce comes to a rolling boil, 1 to 2 minutes. Serve hot. If making up to 1 month ahead, cover and chill.