Bread cubes, ham cubes, bite-size sausage and/or broccoli florets. In a saucepan, melt butter; stir in flour, salt if desired, pepper, mustard, and Worcestershire sauce until smooth. Gradually add milk. Bring to a boil; cook and stir until thickened. Reduce heat. Add the cheese; cook and stir until melted. Transfer to a fondue pot or slow cooker; keep warm. Serve with bread, ham, sausage and/or broccoli.