Melt butter in a 3 quart soup pot. Add shallots and chopped leek and sauté over medium heat until the onions are soft, 5-7 min.
Add the water and chopped potatoes. Bring the mixture to a boil and reduce the heat to a simmer. Simmer the potatoes until tender, 20 min.
Add the greens and herbs and simmer for 10 minutes.
Puree the soup using an immersion blender (or transfer the soup to a traditional blender and blend until smooth). Add the milk, salt and pepper. Mix well.
Serve the soup as is, or topped with sour cream, croutons, or extra herbs.