This is what my roommate in Norway used to prepare for us, except made with perch (silver surfperch, I believe) instead of cod or some other north Atlantic white fish. Some people put enough salt in the water to match the salinity of the sea (2 tbps per quart or per 2 liters), but I wanted to taste the fresh fish without adulteration.
The standard poaching technique could not be simpler: bring cold water, with gilled and gutted fish in it, up to the simmering point and then turn off the heat and let it cook a few minutes more in the hot water. Serve with boiled potatoes and raw onion for an authentic Norwegian meal. (Sour cream and akevitt are optional.)