Peel and finely chop the onion. Clean, wash and slice the mushrooms and sprinkle with 1 tablespoon lime juice. Peel, wash and coarsely chop the potatoes. Heat the fat in a pot. Brown onions and mushrooms in it. Take out 2 tablespoons of mushrooms and set aside.
Add potatoes to the mushrooms, sauté briefly and add 1/4 litre of broth. Bring everything to the boil, cover and cook for about 20 minutes. In the meantime, bring the remaining stock, 1/8 litre water, bay leaf, peppercorns and wine to the boil. Wash the fish, cut into 6 strips and cook in the stock for 6 minutes at low heat. Wash the chives and cut into small rolls. Mash the potatoes in the stock. Stir in cream and season with salt and pepper. Take the fish out and keep warm. Remove 1/8 litre of the fish stock and boil it up with the remaining mushrooms. Mix starch with a little cold water and thicken the sauce. Season to taste with remaining lime juice and pepper.
Mash the potatoes in the stock. Stir in cream and season with salt and pepper. Take the fish out and keep warm. Remove 1/8 litre of the fish stock and boil it up with the remaining mushrooms. Mix starch with a little cold water and thicken the sauce. Season to taste with remaining lime juice and pepper. Arrange mashed potatoes, fish and sauce on plates and sprinkle with chives. Garnish with dill and lime slices