Bring a large pot of water to the boil over high heat. Immerse bones in water and blanch for 2 minutes, then drain well.
Combine bones with 2.5litres (80fl oz / 10cups) fresh water in a large pot. Bring to a boil over medium heat. Skim off any scum that rises. Lower heat to medium-low, cover pot, leaving lid slightly ajar and simmer very gently for 1½–2 hours, skimming occasionally.
Strain stock through a very fine mesh metal sieve. It is ready for use.
Neutral flavoured stock that can be used as a base for soups, in stews or congee. Splash some into the wok when stir-frying vegetables or meat to add a little flavour. It can be refrigerated for a couple of days, or frozen for up to 1 month. Beyond that, its flavour may begin to deteriorate.