Peel and cut into in small pieces or grate vegetables for marinade. Place half the vegetables in a large enough container. Sprinkle fish fillets with chopped dill, lemon juice and brandy from all sides. Place fish fillets on top of the layer vegetables and cover tightly with other vegetables. Cover the container with household foil and place in refrigerator for 24 hours. Heat the butter in a pan and fry the flour. Gradually add broth, stirring fish and marinade and cook over low heat, stirring for about 10 minutes. Shortly before serving, add the cream and some chopped dill to the sauce and mix. Stew fish fillets in a little salted water for about 10 minutes. Remove and transfer to serving plates. Pour the sauce and garnish with lemon slices and a sprig of dill. Serve with boiled potatoes.