The flavor intensity of watercress can vary, so the amount needed for this soup will vary, too, depending on whether you like a strong or mild watercress taste.
3 tablespoons olive oil
2 medium onions, thinly sliced
1 large leek (white and pale green parts only), thinly sliced
4 cups vegetable broth
1 large bunch or 2 medium bunches watercress, thick stems removed (about 4 cups)
1 cup half and half
Green Onion Cream
1/4 cup crème fraiche
2 green onions, thinly sliced; dark green parts reserved for garnish
1 tablespoon grated lemon peel
2 teaspoons grated lemon juice
1/4 teaspoon Worcestershire sauce
1. Heat oil in heavy large saucepan over medium heat. Add onions and sauté until soft, stirring often, about 10 minutes. Add leek and sauté 5 minutes. Add vegetable broth and bring to boil. Reduce heat to low, cover, and simmer 10 minutes. Allow broth mixture to cool uncovered 15 minutes.
2. Place 3 cups watercress in blender. Pour half of warm broth mixture over watercress and blend until smooth. Add half and half and blend until combined.
3. Transfer soup to bowl. Puree remaining broth mixture in blender until smooth; stir into soup in bowl. If stronger watercress flavor is desired, puree ? cup watercress with 2 cups soup in same blender. Repeat with more watercress, if desired. Season soup to taste with salt and pepper. Cover and chill until cold, at least 4 hours. (Can be made 1 day ahead (though L&R found it was definitely better on day 1!) Keep refrigerated.)
For Green Onion Cream:
1. Mix crème fraiche, white and pale green parts of green onions, and all remaining ingredients in small bowl. (Can be made 1 day ahead. Cover and chill.)
2. Divide soup among 6 shallow bowls. Spoon on green onion cream; sprinkle with dark green onion tops.
*As a variation on this recipe, try replacing the watercress with 2 c. of any chopped leafy green vegetable, such as Chinese cabbage, spinach, or chard.