Trim the fish and place in a large frying pan. Add sufficient milk to cover and add the butter in small pieces.
Place the pan over gentle heat and simmer for 5–7 minutes to heat the fish through. Lift the fish from the pan and keep hot. Crack the eggs one at a time first into a teacup then tip into the hot milk in the frying pan. Add all four eggs and poach gently in the hot milk until