Put
the potatoes and onion in a large pot with the water and cook until the potatoes are almost soft.
Lay the Finnan haddock on top
Put the lid on the pot and cook for a further 5 minutes, until the fish is just cooked.
Remove the fish, skin, bone and flake the flesh.
Partially mash the potatoes and onions in the cooking liquor (some prefer a "lumpy" soup while others like a smoother base).
Return the flaked fish to the pot and mix thoroughly
Add enough milk to create the desired consistency, either a thickish stew-soup or a thinner soup.
Season the Cullen Skink