Cut the tomatoes in half and place in a saucepan with the rest of the ingredients over a low heat. Put a lid on the pan and leave to simmer for 10 minutes. Allow to cool, then put through a sieve. Discard the vegetable debris and reheat the liquid. If the resulting sauce, after sieving, is too thin, reduce a little by raising the heat and removing the lid. This also applies to all the variations.