This is my Grandma's recipe, I've altered each time I've made it to suit those whom I'm serving. My Grandma passed away in 2006 but this was one of my favorites that she used to make in the winter time.
Combine potatoes, onions, celery, water and salt. Cook until tender. Do not drain.
Melt margarine in heavy saucepan. Blend in flour, mustard and pepper until smooth. Add milk and cook until thick and smooth, stirring constantly.
Blend in Worcestershire sauce and cheese. Add to potato mixture. Add parsley and tomatoes. Heat thoroughly but do not boil. It is best if cheese is completely melted in white sauce before two mixtures are combined. I like to use the Crockpot to keep chowder hot after it is all mixed.