Bring a large stock pot of water to a boil. Next to it, fill another stock pot or bucket with ice water.
Peel the tomatoes by taking a sharp knife and cutting cross marks on the bottom of each tomato. Once the water comes to a boil, add the tomatoes to the pot a few at a time. Don't overcrowd them.
After a few minutes, the skins start to pucker and draw away from the tomato. Remove them from the pot with a slotted spoon and immediately plunge them into the ice water. Let the tomatoes sit for a few minutes, then transfer them to a large bowl and set aside. Continue with the rest of the tomatoes.
Once the boiled tomatoes are cool enough that you can handle them with bare hands, begin removing the skins. They should peel right off with ease. Discard the tomato skins.
Next, cut the tomatoes in half. Remove the core and discard. Remove the seeds and squeeze as much juice out of the tomato as you can.
At this point, you can put the the tomatoes in jars to can as-is. However, I like to cut them down further into diced tomatoes.
Add 2 tablespoons of BOTTLED lemon juice to the bottom of each quart jar. If using pint jars, add 1 tablespoon of bottled lemon juice to each jar..
Pack tomatoes into the jars. Use the back of a spoon to push out any air pockets if necessary. Fill the leaving 1/2-inch of headspace.
Once you've packed the jars, wipe the rims with a clean damp cloth.
Heat a small pan of water on the stove at a low simmer, but DON'T bring it to a boil. Add your jar lids and let them simmer for a few minutes to activate the glue on the bottom of the lid.
Carefully lift the lids one at a time and place them on top of your jars. Secure the lids in place with rings. Screw the rings on just tight enough to hold the lid in place.
If water bath canning, place the jars in a stock pot deep enough to cover the jars with 1-2 inches of water. Bring the water to a boil then process, covered, for 85 minutes. Once time is up, remove the pot from the burner and allow the jars to sit in the canner for five minutes before removing them. Place the processed jars on a clean towel on the counter or somewhere out of the way and allow them to cool for 24 hours.
If pressure canning, be sure to follow the instructions that came with your canner. Once the processing time is over, let the jar cool for a few hours in the canner.
After the jars have cooled, remove the bands and check the seal on each jar. The lids should be concave and not flex when pushed gently with your finger. If a jar hasn't properly sealed, it's okay to eat. But you'll need to store it in the fridge and use it within a few days.
Properly sealed jars can be store in a cool, dry place for up to 18 months.