Creamy Watercress Soup with Croutons
Rinse watercress and remove thick stems. Set aside a few leaves for garnish.
Peel and finely chop onion. In a pot, cook onion in butter until translucent. Sprinkle onion with flour and cook until flour darkens slightly. Gradually add vegetable stock, stirring constantly. Simmer a few minutes. Stir in watercress and puree soup until smooth. Stir in cream, bring to a boil again and remove from heat.
Whisk egg yolk with a ladleful of soup, then return mixture to pot and stir well. Season with salt, pepper and lemon juice. Cut the bread into small cubes. In a pan, fry bread cubes in oil. Ladle the soup into bowls and serve garnished with croutons and reserved watercress leaves.