Peel and wash the potatoes and parsley roots and cut into pieces or slices. Cook in boiling salted water for about 25 minutes. In the meantime cut bacon into fine cubes. Clean, clean and slice the mushrooms.
Wash parsley, shake dry and cut into strips. Wash fish and pat dry. Season flour with salt and pepper. Leave the bacon out in a pan without fat, take it out. Add mushrooms to the frying fat, fry them while turning them.
Mix in the bacon and season with salt and pepper. Add parsley. Turn the fish in flour, tap off a little. Heat the oil in a pan and fry the fish for about 3 minutes on each side. Heat milk and butter in a saucepan.
Drain the potato and parsley root vegetables. Take out a few slices of parsley root. Add the milk-butter mixture to the potatoes and mash them. Season to taste with salt and nutmeg. Arrange puree with slices of parsley root, fish and mushrooms on plates.