Mastering the Art of French Cooking: Potage Crème de Cresson (Cream of Watercress Soup)

My mom was a little wary of this soup, as we have never had watercress. I know it's some fancy herb they add to salads at overpriced restaurants, but I've never actually eaten it. I managed to find some at the specialty market, but I couldn't make the soup until a week after I had bought the watercress. By that point, half the watercress was yellow or turning to slime, so I was afraid I'd have to trash the stuff and start over. Luckily I was able to rescue just enough tender green leaves to complete the soup.

Potage Crème de Cresson (Cream of Watercress Soup)
From Mastering the Art of French Cooking by Julia Child, Louisette Bertholle, and Simone Beck

⅓ cup minced green onions, or yellow onions
3 tablespoons unsalted butter
3 to 4 packed cups of fresh watercress leaves and tender stems, washed and dried in a towel
½ teaspoon sea salt
3 tablespoons all-purpose flour
5½ cups boiling white stock or canned chicken broth
2 large egg yolks
½ cup whipping cream
1 to 2 tablespoons softened unsalted butter

Cook the onions slowly in the butter in a covered saucepan for 5 to 10 minutes, until tender and translucent but not browned.  Stir in the watercress and salt, cover, and cook slowly for about 5 minutes or until the leaves are tender and wilted. Sprinkle in the flour and stir over moderate heat for 3 minutes.  Off heat, beat in the boiling stock. Simmer for 5 minutes, then puree through a food mill.  Return to saucepan and correct seasoning.

Blend the yolks and cream in a mixing bowl. Beat a cupful of hot soup into them by driblets. Gradually beat in the rest of the soup in a thin stream. Return soup to saucepan and stir over moderate heat for a minute or two to poach the egg yolks, but do not bring the soup to a simmer. Off heat, stir in the enrichment butter a tablespoon at a time.

Makes 6 servings