Prepare Your Mason Jars: Wash, rinse, and sterilize your canning jars by submerging them in boiling water for 10 minutes. Keep them in hot (not boiling) water until ready to use.

Prepare the Tomatoes: Wash the tomatoes and make a small X-shaped slit on the bottom of each one. Blanch the tomatoes in boiling water for about 30 seconds to 1 minute until the skins start to peel away. Transfer them to an ice water bath to stop the cooking process. Peel off the tomato skins, remove the cores, and set aside.

Prepare the Canning Liquid: In a separate pot, heat enough water to cover your tomatoes to a simmer. For each quart-sized jar, add 1 tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid and 1 teaspoon of canning salt (if using). Stir to dissolve.

Fill the Jars: Place a canning funnel on top of a jar. Pack the peeled tomatoes into the jars, leaving about 1/2-inch headspace at the top. Pour the hot lemon juice or citric acid solution over the tomatoes, ensuring the recommended 1/2-inch headspace.

Remove Air Bubbles: Slide a clean spatula or chopstick between the tomatoes and the jar's inner wall to release trapped air bubbles.

Wipe Jar Rims and Apply Lids: Using a clean, damp cloth or paper towel, wipe the jar rims to remove any residue. Place a sterilized lid on each jar and secure it with a band, tightening it until it's fingertip-tight.

Process in a Water Bath Canner: Place a rack in your large stockpot or water bath canner. Arrange the filled jars on the rack, ensuring they are not touching. Add enough hot water to the canner to cover the jars by at least 1-2 inches.

Bring to a Boil and Process: Cover the canner and bring the water to a rolling boil. Once boiling, start the timer for 40-45 minutes (adjust for altitude if necessary). Maintain a gentle boil throughout the processing time.

Remove and Cool: Turn off the heat and carefully remove the jars from the canner using a jar lifter. Place the jars on a clean towel or cooling rack to cool. Leave them undisturbed for 12-24 hours.

Check Seals and Store: After cooling, check the jars for sealed lids. The lids should be concave and not move when pressed in the center. Any unsealed jars should be refrigerated and consumed within a few days. Label the sealed jars with the date and store them in a cool, dark, and dry place.