Rinse the fish and cut into pieces. Place in a saucepan and add the milk, water, lemon slice and bay leaf. Cover and simmer gently until tender – about 15 minutes. Strain off the liquor and reserve
Melt the butter in a saucepan and stir in the flour. Cook gently for a moment, then gradually stir in the reserved fish liquor. Beat well all the time to get a smooth sauce and bring up to the boil. Simmer gently for 2–3 minutes, then draw off the heat. Fold in the flaked fish and then add any one of the following flavourings:
Turn the mixture into a greased pie dish. Cover with the well-seasoned creamed potato. Fork up the top and dot with butter. When ready to serve, place near the top of a moderately hot oven (190 °C., 375 °F., Gas Mark 5) for about 20 minutes. Brown under the grill for a few seconds and serve.