Tarragon lends a subtle flavor to this smooth essence of asparagus.
1. Melt the butter in a large saucepan. Add the onions and toss to coat. Stir over medium heat until the onions are tender. Sprinkle on the flour and continue stirring over medium heat until the mixture foams. Stir in the water and bring to a boil. Add the asparagus and tarragon and reduce the heat. Cover and cook at a gentle bubble for 10 minutes or until the asparagus is tender.
2. Transfer the asparagus with its cooking liquid to a food mill and process to eliminate the asparagus strings, then press through a sieve to smooth out the consistency. Stir in the lemon juice. Cover and refrigerate until thoroughly chilled. Just before serving, blend in the cream and season with salt and pepper. Ladle into glass soup bowls and garnish with sprigs of fresh tarragon.