2. In a saucepan, fry the onions, then add the flaked cod.
3. To make the white sauce, mix the margarine, flour and milk together, then add the remaining ingredients. Make sure the sauce has a runny consistency as it will thicken later when mixed with the other ingredients.
4. Add the white sauce to the cod. Then add the matchstick potatoes.
5. Pour the mixture into an ovenproof dish and heat in a fairly hot oven until golden brown.