Simmer all ingredients, covered, in a large heavy enamel or stainless steel kettle over moderate heat about 40 minutes, stirring occasionally, until tomatoes have cooked down to juice. Put mixture through a food mill or press through a fine sieve, forcing out as much juice as possible.
Return strained juice to kettle and bring to a boil. Pour into 4 (1-quart) hot canning jars, filling each to within 1 inch of top. Wipe rims and seal. Process for 30 minutes at 10 pounds of pressure.