Wash the fish thoroughly, dab dry with kitchen paper, cut into cubes, sprinkle with salt and sprinkle with lemon juice. Clean the asparagus (only cut off the lower ends of the asparagus) and cut in half as desired. Cook the asparagus in boiling salted water for about 10 minutes, then drain well on a sieve. For the sauce, put 125 ml water and cream in a saucepan. Stir in sauce powder with a whisk and bring to the boil. At the lowest setting, gradually beat butter into pieces.
Stir in mustard. Place the asparagus and salmon pieces in a greased ovenproof dish and pour the sauce evenly over them. Bake the casserole in a preheated oven (electric: 200 °C/ gas: level 3) for 20-25 minutes. Serve garnished with lemon and dill. Serve with fine ribbon noodles