Desalinate the cod for 24 hours or more in deep water with frequent changes of water.
Cover in cold water and bring to the boil. As soon as it has boiled take it off the heat. Leave it to cool a bit. Take out all the bones – this may require a knife as well as tweezers. Strip off the skin.
Put the fish into a processor. Whizz. Gradually add the oil. Eat on croutons.