Place all the meat and bones in a large pot and add carrots, celery stalks and tomatoes. Stud the onion with cloves and add to pot. Remove the very outside of the Parmesan rind and discard, add the rind to the pot. Add cold water, 4L or enough to submerge everything by 15cm. Bring to the boil, then turn down the heat and simmer for 3 hours. Add salt during the last 10 minutes of cooking.
When the meat and chicken is so soft that it falls off the bones, turn off the heat and let everything cool in the pot. Store in the fridge overnight. Discard the thick layer of fat that has formed on the top. Strain the stock and refrigerate or freeze.