Rinse the asparagus, peel the white spears completely and cut off the ends. Peel the lower third from the green asparagus and cut off the ends.
Boil 2 liters of water (approximately 8 1/2 cups) with the butter, salt and sugar. Cook the white asparagus for 18 minutes and the green asparagus for about 12 minutes. Drain well.
For the dressing, mix both types of vinegar with the oil and season with salt and pepper.
Arrange the asparagus decoratively on plates and drizzle with the dressing. Serve immediately and garnished with chervil leaves.