Soupe de Cresson

My grandmother made an amazing soupe de cresson and I have been looking for years to recreate this taste from my childhood. For the past few years, I have bought and brought back from France packages of Liebig's watercress soup but I felt it was finally time for me to make my own watercress soup. After trying out many different recipes, I settled on a version of this Epicurious recipe.

4 cups (packed) watercress, stems trimmed
2 tablespoons (1/4 stick) butter
2 russet potatoes, peeled, sliced into 1/4-inch-thick rounds
3 large leeks (white and pale green parts only), sliced
6 cups (or more) canned low-salt chicken broth
1/2 cup whipping cream
3 tablespoons minced fresh chives
Crème fraîche (around $3.99 at Whole Foods or Cowgirl Creamery)

Blanch watercress in pot of boiling salted water 30 seconds. Drain & set aside. Melt butter in heavy pot over medium heat. Add potatoes and leeks; sauté 4 minutes. Add 6 cups broth. Bring to boil. Reduce heat; cover partially and simmer until the vegetables are tender, about 20 minutes. Add watercress and simmer uncovered 5 minutes. Cool 10 minutes.

Working in batches, purée soup in a blender until it has a nice green color and is smooth. Return soup to pot. Mix in the cream. Season with salt and pepper. This soup can be served chilled (in which case, it should be chilled for at least 4 hours before serving) or hot. If served hot, top with a dollop of crème fraîche and snips of chives. Accompany with a salad, or tartines of buttered baguette.