Wash the basil, and then wash and chop the tomatoes.
Arrange the tomatoes in a large pan. If you like, add the basil.
Put the pot with the tomatoes (and basil) on the stove, mash them with a wooden spoon, and cook over medium heat on a medium stove for about an hour or until the tomatoes are well cooked and soft. Stir occasionally.
Two minutes before turning off the heat, add the salt and stir.
At this point, I let the tomatoes cool for half an hour, but you can proceed immediately or even continue after a few hours or the next day. Strain the tomatoes to remove skins and seeds by collecting the juice in a bowl.
Fill the bottles with juice and seal with the caps.
Place the pan on the stove you will use. Arrange the bottles in the pan by putting a dishcloth between them. Cover with hot water (it helps the water to bring a boil). The water should exceed the height of the bottles by at least 2 cm. While boiling, if the water drops, and it will drop, add more. Turn the stove on high heat, cover it with a lid, and bring it to a boil.
When the water boils, remove the lid and cook over high heat for about 20 minutes. Turn off and let the bottles cool in the water. It will be a long time to wait: it is normal!
Store in the pantry for up to one year.