For the broth:
Place the capon (or chicken) in a large pot with the trimmed celery, carrot and onion, a bay leaf and some peppercorns.
Cook over a very low heat for about 3 hours, regularly skimming off any foam from the surface, then season with salt half way through cooking.
Turn off the heat, remove the meat and vegetables, and add the cinnamon stick to enrich the flavour of the broth. Once cooled, leave in the fridge overnight. The next day, skim the fat off the broth and filter through a fine sieve.