Rinse the tomatoes under cool water and pat dry with a clean kitchen towel. Remove the core and quarter the tomatoes. Place the tomatoes in a large pot, add the half of the salt and two bunches of fresh basil, stir well. Cover with a cheese cloth (or kitchen towel) and leave for about 12 - 16 hours at room temperature. This way the tomatoes will infuse that lovely tomato flavor.
Cook the tomato puree
Remove and discard the basil (or even better, use it in another dish). Place your pot over high heat and bring to a boil, stirring occasionally. Reduce the heat to medium-low and simmer for about 2 - 3 hours or until there's about 1/3 of the mixture left. Stir occasionally. Add the rest of the salt, stir to combine.
Preheat the oven to 100°C / 210°F. Place your jars and lids in a roasting pan and place in the oven for 15 minutes. Pass tomatoes through a strainer over a large bowl and season to taste with the rest of the salt.
Pour the tomato puree into jars
Pour the tomato puree into your jars. Set the lids on the jars and close tightly. Wrap the jars into a kitchen towel and let them cool slowly, for about 12 hours. Then store in a cold, dark place for up to a year or use immediately. Enjoy.