Wash the tomatoes. Bring a pot of salted water to a boil. Blanch the tomatoes for 1-2 min., take them out and peel. Grind the vegetables through a very fine milling machine (seed separator is even better).
Pour the resulting paste in a pot, add salt and sugar to taste. Boil the paste to the desired density.
Distribute the mixture into dry jars, close them and sterilize for about 15 min.