Melt the butter and sweat the onions in a covered saucepan until golden brown. Skin the cod and cut into portions. Season with salt and freshly ground pepper. Put into a wide saucepan or frying pan, cover with milk and cream, bring to the boil and simmer gently for 4–6 minutes, depending on the thickness of the fish. Remove the fish carefully to a serving dish. Add the flour to the onions, stir and cook for 2 minutes. Add in the hot milk and bring back to the boil, then simmer for 3–4 minutes. Add the mustard and chopped parsley; taste and correct the seasoning, then pour over the fish and serve.
Duchesse potato may be piped around this dish. It may be allowed to cool and then reheated later in a moderate oven, 180°C/350°F/Gas 4, for approximately 20 minutes.
© 2001 Darina Allen. All rights reserved.