After they're washed, cut them in half and then half again. Put tomato pieces in a pot and set the heat to medium-high; cook for 5 minutes. Cooking will release the juices from the tomatoes therefore there's no need to add any other liquid.
Reduce the heat to medium-low and cook for 15 minutes, breaking down the pieces with the tip of a spoon or spatula.
Remove from the heat and transfer to the jar of a blender. Add salt, put the lid on and process for 30 seconds.
From here, there are two options; passe the mixture through a fine sieve over a bowl and discard the seeds and skins or --
Use it as is or transfer to containers for later use. It makes about 3 cups.