Put 1 kg (2 lb 4 oz) chicken carcasses into a stockpot with a bouquet garni, 1 quartered onion, 1 chopped carrot and 10 peppercorns.
Add 4 litres (16 cups) cold water and bring to the boil. When the stock boils, turn it down to a simmer and skim off the scum.
Skim regularly — adding a little cold water to the pot will help any impurities rise up to the surface so they can be lifted off.
Strain the stock and remove any fat by dragging a sheet of paper towel over the stock surface.
If not using immediately, cool in the fridge. When cool, lift off any congealed fat.
Once made, a stock can be reduced (by boiling) for freezing. The stock can then be poured into ice cube trays and frozen. Reconstitute with water before use. Store stock in the fridge for up to 3 days, or frozen for up to 6 months.