Pour the milk and the water into a large frying pan to about 1" (2.5cm) deep (about 50% milk and 50% water). Warm to just below simmering then place the haddock portions in the liquid with the flesh side down (skin up!). Poach at just below simmering point point for 2-3 minutes then turn the fish over and poach the other side for a further 4-5 minutes. Remove from the pan and allow to drain for a few moments. Just before serving, place a knob of butter on top of the haddock and allow it to melt into the fish. Serve hot.