Cut the haddock fillets in half and place in a pan with the milk, bay leaves and peppercorns. Bring to the boil and then allow to infuse with the heat off and a lid on.
Fry the onion on a low heat in a pan with some butter. Add the carrot, swede and potato to the onion and fry in the pan with the mustard seeds and turmeric, until lightly browned.
Remove the haddock from the milk, set aside and reserve the milk.
Scatter the flour over the vegetables and cook for a couple of minutes. Pour the infused milk over the vegetables with the heat on and stir continuously until you are left with a thick sauce. Cook the vegetables in this sauce until they are soft.
Return the haddock to the pan to warm through and then add the chopped parsley before serving.