Cut the tomatoes into pieces, peel the onions and garlic cloves & cut into small pieces. Put everything in a large saucepan and simmer with all the other ingredients for about an hour. Then brush through a fine sieve into a second saucepan, squeezing out all residues well. Bring to the boil again and pour into glasses or bottles while hot.
Tip: Ketchup can be kept cool and dark for up to six months.