While macaroni is cooking, melt butter in 3-quart saucepan over low heat. Stir in flour, salt, pepper, mustard and Worcestershire sauce. Cook over medium low heat, stirring constantly, until mixture is smooth and bubbly; remove from heat. Stir in milk. Heat to boiling, stirring constanly. Boil and stir 1 minute. Stir in cheese. Cook, stirring occasionally, until cheese is melted.