Peel, wash and slice the potatoes. Layer roof tiles in a greased gratin dish. Peel onions and garlic. Chop 1 onion and garlic. Spread on the potatoes, season. Pour cream over them, sprinkle with parmesan. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/gas: level 3) for about 45 minutes
Quarter the remaining onion. Boil up with fish stock, champagne, ci- trone, bay leaf, peppercorns and a little salt. Simmer for about 4 minutes.
Dice 50 g butter and freeze briefly. Wash the salmon, dab dry and cut into 4 pieces. Season with a little salt and pepper. Fry briefly on each side in 1 tablespoon butter. Add 5-6 tablespoons of fish stock. Cover and steam over medium heat for about 6 minutes. Carefully lift out the salmon, keep warm
Sud to the remaining stock seven. Reduce everything to half. Whip the butter cubes bit by bit. Season to taste the sauce. Serve everything