Peel the asparagus, cutting off the woody ends. Wash the asparagus and cut into pieces. Cook in boiling salted water with some sugar for about 10 minutes. Peel onion and cut into cubes.
Add to the asparagus 1 minute before the end of the cooking time and cook briefly. Drain the asparagus on a sieve and let it cool down. In the meantime, wash the chives and parsley and dab dry. Cut the chives into small rolls.
Pluck parsley leaves from the stalks and chop finely. Mix vinegar, lemon juice and herbs and season with salt, pepper and sugar. Whip the oil into it. Pour marinade over the asparagus and leave to marinate for approx. 30 minutes.
Arrange on plates and serve garnished with parsley as desired. Serve with toast and chive butter.