Wash empty canning jars in hot, soapy water, and rinse them thoroughly. Or run them through the dishwasher. Place jars in boiling water.
Cover the jars with hot water; bring to a simmer over medium heat.
Let the jars simmer for 10 minutes. When ready to start filling, place jars on a clean kitchen towel to prevent them from slipping. Let jars air dry.
Start with firm, unblemished tomatoes, and wash them well in cold water.
To remove the skins, dip tomatoes in boiling water for 30 seconds or until the skins start to split. Immediately place the tomatoes in cold water.
When cool enough to handle, remove the skin and core with a paring knife or manually. If desired, cut the tomatoes in half and remove seeds at this time.
When filling the jars pay attention to headspace as overfilling or underfilling the jars will negatively affect the seal during processing. To overcome this challenge, use a wide-mouth funnel in the cleaned quart size canning jar to get the liquid level just right.
First ladle whole or halved tomatoes into the jars, along with any juices from preparing the tomatoes, pressing to fill spaces with juice.
Next use the funnel to add bottled lemon juice and salt (1 tablespoon lemon juice and 1 teaspoon salt for quarts). Leave ½-inch headspace.
Once the jars are filled, wipe the jar rim with a clean, damp towel to remove all traces of food. Food on the rim prevents a perfect seal.
Position the prepared lid and screw band on the jar and tighten according to the manufacturer's instructions.
Set each jar into a canner or large pot as it fills with water. The jars should not touch. Cover the pot.
Process the tomatoes in boiling-water for 85 minutes. Begin timing when the water starts boiling.
Carefully remove the jars from the pot. Cover the jars with a clean tablecloth, and allow them to cool at room temperature.
Test the seals to ensure proper processing, label the jars with the date, and store in a cool, dark place (like a pantry) to enjoy for up to a year.