My mother was a great soup and gravy maker and her secret was a good strong stock. She would get unwanted bones from the butcher, use left over bones and meat from the weekend joint and add home grown onions and any vegetable left overs that were around and put them in a pressure cooker. Fill it 2/3rds full of water and cook at full pressure for a couple of hours making sure that the cooker did not boil dry.
Reduce the pressure and strain the liquid ready to form the base of a soup, gravy or casserole.
It is usually possible to do a second boiling but this time for around one hour only.
Discard the left overs to the compost heap.
My sons accepted that whatever they left on their plates, or scraps of the joint went straight into the stock pot. Others on camp would look rather strangely as the bones all went into the pot. A good boiling avoided any risk of contamination but the boys certainly lived well on Chris's Cuisine.