You will need:

  Large stew-style pot
  Fine mesh colander
  Chopping board
  Good knife

Ingredients:

  3kg approx. (7lb) of bones including connective tissues, fat, cartilage, meat etc
  4 sticks of celery chopped into quarters
  4 unpeeled carrots chopped into quarters
  1 leek chopped into quarters (the white part only)
  2 TBSP apple cider vinegar
  Water (enough to cover everything)
  Himalayan salt to taste (I use ½ TBSP)
  Black pepper corns to taste (I used a good TBSP)

NOTES:

 If you intend on feeding some left overs to your pet, then take the solids you want out of the pot at the end, then only add the leek, salt, and pepper afterwards for the last hour or so of cooking.
 Using organic meat, bones, and vegetables where possible, as well as filtered water, is ideal – but not mandatory.
 Adding herbs such as parsley or rosemary are optional and I never really noticed a huge difference in taste when I did.

Step 1. Put all ingredients in the pot and cover with water. Ensure the water is at least a few inches from the top of the pot as it can easily boil over.

Step 2. Allow to slowly bring to the boil, then reduce to a simmer immediately.

Step 3. Let simmer for 24 hours, then check the taste. If you are happy with the flavour, and are discarding the solids afterwards, then strain through the colander into heat-proof jars or containers and let cool to room temperature before putting in the fridge or freezer.
* Glass jars can easily break when put straight into the cold. I learnt this the hard way!

Step 4. It is optional to cook for longer, up to 72 hours. I personally found the taste was at its best between 24 and 36 hours.