Peel the asparagus, cut off the woody end. Boil up plenty of water with salt and a little sugar. Add the asparagus and cook for about 15 minutes in lightly boiling water. In the meantime, for the mustard vinaigrette, stir lemon juice, mustard and 2 tablespoons of cold water until smooth.
Add oil. Wash the dill, dab dry and chop. Add to the vinaigrette. Season to taste with salt and pepper. Drain the asparagus and rinse with cold water, cut into pieces and mix with the vinaigrette.
Let it cool down a little. Peel, wash and roughly slice the potatoes. Season with salt and fry small Rösti in hot fat, spoon by spoon, on both sides until golden brown. Arrange three to four Rösti with lukewarm asparagus salad and a slice of salmon on each plate.
Garnish as desired with lemon wedges and dill.