Cut into 4 portions of chicken fry in 3 tbsp butter with chopped onion and 1-2 tbsp water. When remain of butter, sprinkle with flour and stir until fry until golden. Gradually pour the champagne and boil 20 minutes with the lid on low heat. Mushrooms cut and fry in remaining butter. Add to the meat 20 minutes before it's ready. Mix the cream and the egg yolks and the sauce boil. It flooded portions serving. Sprinkle with chopped parsley.