Peel and slice the onions and slice the carrots and celery. Place all the ingredients in a large pan, bring to the boil, then cover with a lid and simmer for 20 minutes. Allow the stock to cool a little, then strain through a fine sieve (strainer) and discard all the solids. This produces about 3 pints (1.8ltr) of delicate Court Bouillon that will keep in a freezer until required. A little time taken but the difference in flavour to our cooking will make it well worthwhile.