Place the haddock, skin side down, in a large shallow pan, pour over the milk and water, then add the peppercorns and bay leaves.
Bring to the boil, then lower the heat and simmer for 10 minutes or until the fish can easily be separated from its skin. Reserve the cooking liquid.
Peel the skin from the haddock, break the flesh into large flakes, then cover and set aside. In another, deeper pan, simmer the lentils in deep water for 15-20 minutes till buttery and tender. Drain and set aside.
Wipe the pan the lentils were cooked in and place over a moderate heat. Melt the butter in the pan then add the rice.
Ladle 800ml of the cooking liquid from the fish into the rice, ladle by ladle, stirring almost continually, as if you were making a risotto. Season with salt and a little pepper. Chop the dill.
As soon as the rice is tender and to your liking (probably about 15-20 minutes) stir in the cooked lentils, the chopped dill, the butter and then, lastly, the flaked haddock.