Potage Parmentier - Potato Leek Soup

0 In a large heavy bottom pot over medium heat, melt the butter. Add the leek and sauté until the leeks are soft, 4 minutes.  
1 Add the potatoes and cook for a couple of minutes.  Add the water and salt and partially cover cooking at medium heat for 30 to 40 minutes or until the vegetables are nice and tender.
2 With an immersion blender or food mill, mash all the vegetables to a rich paste-like consistency.
3 Off the heat, and just before serving into the soup bowl add the whipping cream and stir well. 
4 Ladle on bowls, place a dollop of crème Fraiche in the middle, and sprinkle the chive over it.