For those that have asked: they have a simple recipe for stock, which the Americans call bone broth.
This is 101 in any restaurant kitchen that I have ever worked in and made once or twice every week by an apprentice.
3 kg of beef bones, lamb bones or chicken carcasses.
1. Place bones in large stainless steel pot, slow cooker of pressure cooker and cover with cold water, the water should cover the bones by 5 cm while leaving room at the top of the pan.
2. Cover with lid and bring to the boil, then reduce the heat and simmer with the lid on for at least 12 hrs. for beef or lamb and 6 hrs. for chicken. If using a slow cooker, cook on high for at least 12 hours. If using a pressure cooker cook on high pressure for at least 3 hrs.
3. Strain the liquid, using a fine mesh for strainer for the chicken. Use immediately or leave to cool before storing. Bone broth will keep in the fridge or several days.
Optional extras: generous splash of apple cider vinegar or lemon juice, onion, leek, carrot or celery, parsley stalks peppercorns and or bay leaves.