I had meant to try this soup for years and the stars finally aligned this holiday season–I had good watercress and I remembered to try the recipe (from The Soups of France, by Lois Anne Rothert, p 38) simultaneously. Of course I had to significantly alter the recipe for my dietary restrictions. The original recipe calls for watercress, butter, shallots, potatoes, water, salt, milk, sour cream, and parsley or chervil.
Here is my (very different) nondairy version:
2 bunches watercress, large stems removed
2 – 3 Tbs olive oil or other fat of choice
2 leeks, white and pale green parts chopped
4 – 6 cups chicken broth
1 tsp salt
Coarsely chop the watercress leaves. Heat the oil in a heavy soup pot over low heat. Simmer the leeks until softened. Add the watercress, broth; add additional water to cover if needed. Simmer until the leeks and watercress are soft (15 – 20 minutes). Using a handheld blender blend a bit so that there are still some chunks left in the soup. Add salt to taste.