Remove any excess fat from the chicken carcasses and wash thoroughly under cold running water. Place in a stockpot with the remaining ingredients and bring to a simmer. Skim immediately, then turn the heat off and allow the bones and vegetables to sink to the bottom of the pot.
Turn the stock back on, skim again and bring it to just under simmering point — there should be as little movement in the pot as possible.
Cook the stock over a very low heat for 12 hours, skimming frequently.
Pass the stock through a fine sieve into a clean pan, discarding the solids. Bring to the boil and reduce until the volume is about 2 litres/3 ½ pints/2 quarts.
In soups, sauces and for braising white meats. It can also be used to cook and finish risotto, but if the stock is very strong it may overpower the risotto’s principal ingredient.
The strength of flavour is determined by how much the basic stock is reduced. Be aware that reducing it too much can make the stock very salty. The end result should be a clear amber liquid with a rich clean taste.
Up to 1 week in the fridge, or up to 1 month in the freezer.