Cook the potatoes for about 20 minutes in salted water and peel them. Peel and chop the onions. Heat vinegar, chicken soup, oil, mustard and diced onions and season with salt, sugar and pepper.
Cut the potatoes into slices. Pour hot stock over them. Cover and leave to stand for approx. 30 minutes. Drain the asparagus. Cut salmon into strips. Wash the dill, dab dry and cut finely except for a little garnish.
Fold everything under the potatoes. Serve garnished with crème fraîche and dill flags.