Cod in mustard sauce

Wash the fish, put in a low saucepan, putting a branch of parsley under each piece of fish so that the fish does not stick to the bottom. Pour milk and water, salt, pepper, put bay leaves. Bring to a boil, cook over minimal heat so that the surface of the liquid barely trembles, about 10 minutes until the fish is ready. Remove the finished fish, let the liquid drain and put the fish in a warm place so that it does not cool down. Melt the oil over fire, add flour, stir, remove from the heat and gradually pour 425 ml of strained fish decoction, constantly stirring until homogeneous. Put the sauce on a heat and bring to a boil with constant stirring. When the sauce thickens, remove from the heat, salt, pepper, add vinegar and mustard, mix. Pour the fish with sauce, sprinkle with parsley greens and serve. Traditionally, this dish is served with a clapshot.