Lúðusúpa - {Icelandic Halibut Soup}

Bring the water to the boil in a pan with vinegar, bay leaves, and some salt. Add the halibut and simmer at low heat until the fish is cooked through and just beginning to come off the bones. Strain most of the stock into a clean pan, add prunes and bring to the boil, but leave half a cup or so in the pan with the fish and keep warm.

Beat the softened butter into the flour, and whisk into the soup to thicken it. Simmer for 5 to 8 minutes, then add lemon juice and sugar and season to taste. Serve the fish on a separate plate but with the soup.

Serve hot in small bowls to 4 with the rest of the meal -- there will be plenty of fish on the side for all.