Trim off bottom ends of white asparagus and peel. Finely dice onion. Juice the lemon.
Add water to a large pot with the lemon juice, sugar, and salt. Bring to a boil. Add the asparagus and simmer for approx. 8 min.
Remove asparagus from the pot and reserve the cooking liquid. Once cool enough to handle, slice the asparagus, and set aside the heads.
Melt butter in a pot and add onions. Sauté over medium-low heat for approx. 1 min. Add flour and stir well. Deglaze the pan with white wine and the reserved asparagus cooking liquid. Add in sliced asparagus stems and whisk in cream. Let the soup simmer for approx. 10 min. more and season with white pepper and salt.
Purée the soup with an immersion blender. Serve garnished with chopped chives and reserved asparagus heads. Enjoy!