For the cress soup, first peel and chop the potatoes and onion.
Sauté both in a little hot oil in a pot and then pour 4 cups of water. Cook for about 15 minutes until soft.
Now add 3/4 of the cress to the soup and puree with a hand blender.
Finally, just season with salt and garnish the cress soup with the remaining cress before serving.