Peel the potatoes and slice them thinly. Chop the onion and put it all in a pot with enough water to cover the potatoes and onion. Place the salmon on top and let it all cook for approx. 15 minutes. (The salmon is on top of the potatoes and is therefore steamed).
Stir up the sauce while it cooks.
When the pot is done cooking, you pour the water from the potatoes, onion and salmon. Let it cool for a while. Then mix everything into the sauce.
Serve with salad or bread (or both).