This is one of the rare recipes where I prefer heavy cream to crème fraîche. The reason? It makes it easier to decorate the soup with a pretty swirl of cream just before serving.
Watercress soup is very quick to prepare and is delicious both hot and chilled. No spice needed, as the watercress is quite piquant on its own — but if you like you can add some chopped fresh herbs just before bringing the soup to the table. The quantities below are for two people. For a larger crowd, double or triple the recipe.
1 bunch watercress (3/4 pound; 330 grams)
1 medium potato
3 cups (3/4 liter) homemade chicken broth, vegetable broth or water
1 pinch dried tarragon
salt and freshly ground black pepper
2 tsp. fresh lemon juice
2 tbsp. crème fraîche or heavy cream
Remove the watercress stems. If your watercress came in a bunch from the market, simply slice through the bunch above the tie. If it’s loose, cut off the thick bottom part of the stems — no need to separate each leaf, as the thinner stems can be blended into the soup.
Wash the watercress carefully: Immerse it in a basin of water, then spin dry in the salad spinner. Repeat.
Peel and cube the potato. Peel and dice the shallot.
Bring the broth or water to a boil. Add the watercress, potato, shallot, tarragon, salt and pepper. Reduce heat to medium and simmer for 20 minutes, until the potato is very tender. Do not cover the pot.
Blend the soup and return to a clean pot. It will be a deep bright green. Add the lemon juice. Taste and adjust the seasonings. Add the cream.
Reheat gently just before serving. Add a swirl or drizzle of heavy cream to each bowl, or set a bowl or pitcher of extra cream on the table. Serves 2.