Start by preparing the cod liver if you have it. Put it into a bowl of water and pull it apart with your fingers, discarding the membranes. Tear the liver up into small pieces, then drain. When you are ready to make the sauce, bring about 300ml of water to the boil with the bay leaf. Add the vinegar and liver and bring back to the boil. Add another 150ml cold water and again bring back to the boil. That's it.

For the cod itself, fill a saucepan large enough to take the roe and steaks with enough water to come about two-thirds of the way up the sides. Add lots of salt, stirring to dissolve. The water should be as salty as sea-water. Wrap the roe in greaseproof paper and place it in the pan. Bring to the boil and simmer for about 10-15 minutes, until the roe is just firm. Add the vinegar and then the cod steaks. Bring slowly back to the boil, let it bubble for 1 minute, then turn off the heat, cover and allow to stand for 5 minutes or so, until the cod is cooked through.

Serve the cod with the liver sauce, reheated if necessary.