In 1-quart saucepan, melt 3 tablespoons of the butter over medium heat. Add onion; cook, stirring frequently, 4 to 5 minutes, or until tender. Stir in flour salt, pepper and nutmeg. Cook and stir until mixture is bubbly. Gradually stir in half-and-half. Heat to boiling, stirring constantly; boil and stir 1 minute. Remove from heat; set aside.