Icelanding fish stew

Ingredients
50 g butter
½-1 dl wheat flour
500 g potatoes, boiled
500 g boiled cod
4 dl milk and fish stock
Salt
Pepper (white or black)
Method
Boil the potatoes. Icelandic potatoes are usually boiled with the skin on, then the skin is removed after boiling. But before removing the skin it is best to cool the potatoes down by letting the hot water run off them and replacing it with cold water for a few minutes. Bring water to boil in a deep, wide pan or pot. Add salt and then the fish, cover with lid. Immediately turn off the heat and leave the pan standing on the stove. In about 8-9 minutes remove the fish from the water, keep the water (stock) to use later. Cut the potatoes into bite size pieces and use a fork to flake the fish. Keep aside.
Having removed both fish and stock from the pan you can now add butter and onion to the pan (remember to turn the stove on again, medium heat). Let it simmer for a little while until the onion turns soft and clear. Stir in the flour and then gradually thin it out with a mix of stock and milk (⅓ stock, ⅔ milk). It should turn to about the thickness of a good gravy or thick soup. Next you can add the cut potatoes and flaked fish and stir it all loosely together. Add salt and pepper to taste. Serve with Icelandic rye bread (the black chunky type) with lots of butter spread on top of each slice.