Put it into hot water, and boil gently for five minutes or longer if the fish is very thick. Take it out of the water and put it on to a hot dish, rub a small piece of cold butter over it and cook for a few minutes either in the oven or in front of the fire. One or two soft boiled eggs broken over it is a nice way of serving it, or a few very thin slices of bacon well cooked may be placed round the dish as a garnish.