Place all the ingredients in a large stock pan, bring to the boil and let simmer for between 12 and 24 hours on low heat. The longer you simmer the more intense the broth will be. The one in the picture was kept simmering for 12 hours. Also of note is that the longer you simmer the broth the less the final quantity will be in terms of volume.
Strain and place the liquid in glass jars and store in the fridge. It will keep in the fridge for at least 5 days or you can freeze the broth for up to 3 months.
Once the broth has cooled you will get a layer of fat settle on the top. You can gently remove this and use it in cooking instead of other oils. It's especially good for roasting vegetables.