Wash, remove stems, and trim tomatoes of any bruised or discolored parts.

Working quickly and with 1 lb. of tomatoes at a time, quarter the tomatoes and place in a large saucepan.

Bring the tomatoes to a boil as you crush them with a potato masher or large spoon.

Continue adding the quartered tomatoes, cutting them up as you work.

Keep mashing the tomatoes over high heat until all pieces have been added.

Let the tomatoes simmer for 5 minutes.

Transfer the heated, crushed tomatoes to a food mill or sieve and remove skins and seeds.

Return the tomatoes back to the saucepan and simmer until the desired texture is achieved. For thin sauce, reduce by one-third and for thick sauce reduce by half.

Prepare jars for canning by adding either 2 tablespoons of bottled lemon juice or 1/2 teaspoon citric acid to each quart-sized jar, or 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid to each pint-sized jar.

Add 1 teaspoon salt per quart or 1/2 teaspoon salt per pint to each jar (if desired).

Ladle the hot tomato sauce into the prepared jars, leaving 1/4-inch headspace.

Seal each jar with 2-part lids and process in a water bath canner for 40 minutes (quarts) or 35 minutes (pints), adjusting the time as needed depending on the altitude (see notes). For pressure cooker settings, see notes.

Give the processed jars 5 minutes to acclimatize before transferring them to a clean towel using a jar lifter.

Arrange the jars lid-side up, without touching, and let them sit for 12 to 24 hours at room temperature.

Remove the rings and check to make sure the lids are sealed. Move any unsealed jars to the fridge.

Label jars with the date and contents. Store in a cool, dry, dark location for up to 18 months.