Bring the stock and wine to the boil and let it boil down over high heat for about 5 minutes
Peel and chop the shallots. Fry in 1 tbsp. hot butter until translucent. Sprinkle with flour and sauté until light brown. Add boiled stock while stirring. Bring to the boil and simmer for about 20 minutes
Wash the fish, pat dry and cut into 8 pieces (slices). Sprinkle with lemon juice. Heat 1 tablespoon butter. Season fish and fry for 4-5 minutes on each side
Whip 2 tablespoons of ice-cold butter in flakes under the sauce. Season sauce with salt, pepper and mustard. Mix egg yolk and some sauce, stir back into the sauce (do not boil any more!). Whip cream until semi-stiff and fold in. Serve everything. Garnish with dill and lemon. Serve with fried or roasted potatoes and cucumber salad