A warming soup for winter night. Blend it in a food processor if you like a smoother texture.
Boil the potatoes in salted water for 5-10 minutes, or until tender. Drain the potatoes and mash until smooth.
Meanwhile, place the fish into a saucepan with the chopped onion and water. Cover and simmer gently for 10-15 minutes or until the fish is tender.
Remove the fish, flake the flesh finely then return it to the pan. Add the milk and bring to the boil then gradually mix in the mashed potato.
Stir in the butter and lemon juice and season to taste with salt and freshly ground black pepper.
Serve with chopped parsley.