2 lb. green asparagus
1 large onion, chopped
3 TBS unsalted butter
5 to 6 cups low-sodium chicken broth
½ cup crème fraiche or heavy cream
¼ tsp. fresh lemon juice, or to taste
Coarse salt and pepper to taste
Fresh snipped chives for garnish
Cut the tips from some of the spears and reserve for garnish. Cut all the remaining asparagus into ½-inch pieces.
Melt butter in a 4-quart heavy pot over moderately low heat. Add chopped onion and cook, stirring frequently, until just softened. Add asparagus pieces, some coarse salt and pepper and continue cooking and stirring for about 5 more minutes. Add 5 cups of broth and simmer, covered, until asparagus is tender, 15 to 20 minutes.
While soup simmers, cook reserved asparagus tips in boiling salted water until just tender, 3 to 4 minutes. Drain and rinse under cool water to stop cooking.
Puree soup in batches in blender until very smooth, and then return to pot. Stir in crème fraiche or heavy cream and more broth, if desired. Season with salt and pepper. Bring soup to a brief boil and whisk in remaining tablespoon of butter.
Just before serving, add the lemon juice. Ladle into bowls and garnish with reserved asparagus tips, snipped chives and a few dribbles of cream. (Note> soup can be made up to two days in advance. Remember do not add lemon juice and last tablespoon of butter until just before serving)