Saute onion, celery and carrots in butter or margarine. Add chicken stock, potatoes and bring to boil. Simmer for 20 minutes until potatoes are soft. Mash potatoes with potato masher to smaller chunks. Add salt, pepper, parsley and tobasco to taste. At end, add evaporated milk. Heat. Do not boil after adding the milk. I also add cooked, crumbled bacon and 1 can creamed corn. You also could add salmon, clams, ham or whatever to make whatever chowder you want!