Core the tomatoes and chop them coarsely. Chop the onions, peppers, celery, and parsley coarsely, and divide equally, along with the tomatoes, between 2 very large, deep kettles. Divide the salt between the 2 kettles, too. Cover, bring to a boil, and simmer over medium-low heat for 1 hour, or until all vegetables are very tender. Stir frequently. Put mixture through a sieve or food mill. Transfer the puree to a large kettle. In a medium bowl, combine all remaining ingredients except butter. Add the seasonings gradually to the hot puree, beating in with a whisk. Add the butter and whisk smooth. Bring to a boil, then simmer over medium low heat for 3 minutes. Pour hot into dozen hot pint jars, leaving 1 cm head space. Seal and process in hotwater bath for 15 min. To serve, add one 11 ounce can cream of mushroom soup and 1 soup can of water to every pint of tomato soup base. Heat and serve NOTE: You can also prepare the soup base by adding 1.5 cups milk to it, or even using 1.5 cups water.