Wash the tomatoes well under running water. Remove the stems and cut a shallow "X" in the bottom of each fruit.

Bring a large saucepan of water to a boil over high heat. As the water is heating, fill a large bowl with ice water.

Once the water comes to a boil, dip your tomatoes into the boiling water until the skins crack and loosen, about 30 to 60 seconds.

Transfer the tomatoes from the boiling water to the bowl of ice water to cool. Repeat for all the tomatoes.

Once the tomatoes are cool enough to handle, remove the skins, scoop out the seeds, and cut out any thick cores.

Cut about 6 tomatoes into quarters, and place these in a large sauce pot.

Bring to a boil over medium-high heat. Stir to prevent sticking, and crush the tomatoes with the back of your spoon once they soften.

Cut the remaining tomatoes in half and add them to the pot as your work. Stir frequently to cook evenly and prevent sticking.

When all the tomatoes have been added, continue to cook, stirring occasionally, until the tomatoes are soft and juicy, about 10 minutes.

Remove the pot from the heat and let the tomatoes cool slightly before pureeing.

Puree the tomatoes using a food processor, food mill, or sieve to smooth out the sauce.

Return the tomato puree to the saucepot and simmer uncovered over medium-low heat for 1 to 2 hours until the sauce thickens and reduces in volume: Reduce by 1/3 for a thin sauce. Reduce by 1/2 for a thick sauce.

While the tomato sauce is cooking, wash the jars, lids, bands, and canning tools in warm, soapy water. Rinse thoroughly, and set aside to air dry on a clean kitchen towel.

Place the water bath canner on the stove. Place the jar rack into the pot, set the jars in the canner, and fill with enough water to cover the jars.

Bring the canner to a simmer (180˚F) for 10 minutes, and keep the jars hot until you are ready to fill them.

Spread a kitchen towel on the counter. Use the jar lifter to remove ONE jar from the canner. Drain the water back into the canner, and place it on the towel. Keep the remaining jars in the canner so they stay hot.

Add 1 tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid to the jar.

Use the canning funnel and ladle to fill the jar with the tomato sauce. Leave a 1/2-inch headspace.

Run the bubble popper through slowly to release any air bubbles. Wipe the rim with a clean, damp towel to remove any residue.

Add the lid and secure it with a screw band until it's fingertip tight.

Return the jar to the canner. Then, repeat with the rest of the jars.

Once the filled jars are all in the canner, adjust the water level so it is at least 2 inches above the tops of the jars.

Cover your canner and bring it to a boil over medium-high heat. Once the water boils vigorously, set a timer and process pints for 35 minutes at altitudes of less than 1,000 ft. Adjust processing time for your altitude if necessary. (See notes.)

When the processing time is complete, turn off the heat, remove the lid, and let the canner cool and settle for about 5 minutes.

Spread a dry kitchen towel on the counter. Then, use the jar lifter to remove the hot jars from the canner and place them on the towel. Keep the jars upright, and don't tighten bands or check the seals yet. Let the jars sit undisturbed for 12 to 24 hours to cool.

After 12 to 24 hours, check to be sure the lids are sealed by pressing on the center of each cover. Refrigerate any jars that fail to seal and consume them within a week.

Yields about 3 to 4 pints depending on how much you reduced your sauce.