Roughly chop the celery, leeks, onions and carrots.
Leaving it unpeeled, bash the half bulb of garlic.
Place the chicken carcasses, garlic, vegetables, herbs and peppercorns in a large, deep-bottomed pan.
Add 6 litres of cold water and bring to the boil, skim, then turn the heat down to a simmer.
Continue to simmer gently for 3-4 hours, skimming as necessary.
Pass the stock through a fine sieve.
Allow to cool for about half an hour, then refrigerate.
Once the stock is cold it should look clear and slightly amber in colour.
Divide it into small plastic containers and freeze it.
It will keep in the fridge for about 4 days and in the freezer for 2-3 months.
