Watercress Soup with Pickled Cucumbers

In a large saucepan, heat the olive oil. Add the leek and cook over moderate heat, stirring, until softened, 3 minutes. Add the broth and water and bring to a boil. Add the potato, cover and simmer over low heat until tender, about 15 minutes. Add the watercress and cook until bright green, about 2 minutes.

Working in batches, puree the soup in a blender. Return the soup to the saucepan. Add the whole and skim milk and season with salt and pepper; keep warm.

Meanwhile, trim the peeled cucumber to form a rectangle. Cut the cucumber crosswise into very thin slices. In a medium bowl, combine the rice vinegar with a large pinch of salt. Add the cucumber slices and toss well. Let stand until they have softened, about 5 minutes.

Ladle the soup into bowls. Garnish with cucumber slices and serve.