Chilled Watercress Soup with Crème Fraîche and Za’atar

In a medium saucepan, combine the potatoes and garlic with 4 cups of water and bring to a boil. Cover and simmer over moderately low heat until the potatoes are tender, about 20 minutes. Add the watercress and cook until the greens are just tender, 2 to 3 minutes. Let cool slightly, then refrigerate until cold.

Transfer the cold potato-watercress mixture to a blender and puree until smooth. With the machine on, drizzle in the olive oil until incorporated. Pour the soup into a large bowl and stir in the buttermilk, whole milk and 1/2 cup of cold water; stir in more water if the soup is too thick. Cover and refrigerate, about 1 hour. Season with salt.

Pour the chilled soup into 8 bowls. Top each with a tablespoon of crème fraîche and 1 teaspoon of za’atar and serve.