Wash tomatoes and dip them in boiling water for 30 to 60 seconds or until the skins split. Dip in cold water and slip off the skins. Remove cores and quarter tomatoes.
Boil the tomatoes for 20 minutes, uncovered, in a large saucepan. Put through a food mill or sieve. Sauté onions, garlic, celery or peppers, and mushrooms (if desired) in vegetable oil until tender. Combine sautéed vegetables, tomatoes, salt, oregano, parsley, black pepper, and sugar. Bring to a boil.
Simmer uncovered, until thick enough for serving. At this time the initial volume will have been reduced by nearly one-half. Stir frequently to avoid burning. Fill jars, leaving 1-inch headspace. Adjust lids.
Dial Gauge Canner - Process at 11 pounds pressure - Pints 20 minutes and Quarts 25 minutes.Weighted Gauge Canner - Process at 10 pounds pressure - Pints 20 minutes and Quarts 25 minutes.
Recipe Tips
Caution: Do not increase the proportion of onions, peppers, or mushrooms. If you do, you will affect the sauce's acidity, and it will be necessary to use a pressure canner.