In a large, thick-walled saucepan, heat 50 g of butter over medium heat, add fish and vegetables and cook until golden brown.
Pour wine and enough water over the contents of a saucepan to cover the fish and vegetables. Put a bouquet of Garni in a saucepan, add salt and pepper to taste. Bring stew to a boil, simmer for about 20-30 minutes, stirring occasionally.
Meanwhile, cook mushrooms and onions. Heat 25 g of butter in a saucepan, add peeled onions, fry until golden brown. Then add mushrooms, fry mushrooms until golden brown. Season with salt and pepper set aside.
Strain the stew through a sieve into a clean saucepan. Remove herbs and peppercorns from a sieve.
Arrange boiled fish and vegetables in portioned plates, set aside.
In a small bowl, mix 15 butter with 1 tablespoon. a spoonful of flour. Bring the broth to a boil. Gradually add the flour crumbs to the boiling broth, stirring constantly (the broth should thicken). Season the broth with salt and pour over the vegetables and fish on the plates. Top with fried onions and mushrooms sprinkle with parsley. Serve the stew immediately.