This is an acquired taste, much like Finnan Haddie, which is also a traditional Icelandic way of preserving haddock, only we call it reykt ýsa (smoked haddock). Because haddock does not take well to salting like it cousin, the cod, it is usually either smoked or “hung” when it needs preserving.
Take one haddock, approx. 1 to 1 1/2 kilo, and remove the head and guts, or ask the fishmonger to do it for you. Do not scrape off the slime.
This is best done in cold but not frosty weather. Hang the fish in the shade for anything from 12-20 days, depending on how big the fish is and how strong you want the flavour to be. Take care not to dry it completely, because then you have made stockfish which requires soaking if you plan to cook it or much beating if you want to eat it raw. Hung haddock should be firm but not dry.
Before cooking, remove the tail and fins and tear off the skin. Cut into pieces and drop into boiling salted water and cook for about 10 minutes. Serve with plain boiled potatoes and butter or tallow, or, if you can get it, the fat that melts from hangikjöt when it is cooked. Also good served with bechamel (white) sauce.