1. Wash the tomatoes and cut them into quarters. Remove seeds if you prefer a smoother paste.2. Place the tomatoes in a large pot and cook over medium heat until they soften, about 10–15 minutes. Stir occasionally.3. Pass the cooked tomatoes through a food mill or sieve to remove skins and any remaining seeds.4. Return the tomato pulp to the pot. Add salt and olive oil.5. Cook over low heat, stirring often, until it reduces into a thick paste. This can take 2–3 hours.6. Let the paste cool completely.7. Spoon into clean jars and cover the top with a thin layer of olive oil. Seal and store in the fridge for up to 3 weeks or freeze for longer storage.