Place the carcass in a saucepan large enough for the bones, veg and about 2.25 litres of water.
Add the water and bring to a very gentle simmer. Don’t boil! This is the secret of perfect clear stock. When white scum rises to the surface, skim it off with a spoon. Add the veg on top of the bones.
Place the pot half on, half off the heat. The gently simmering stock will rise and fall through the veg, which act as a filter, absorbing impurities and leaving the liquid clear. Simmer for 2 hours. When the taste stops improving it’s ready.