In a saucepan over high heat, combine the leeks, potatoes, and stock. Bring to a boil, reduce the heat to medium-low, cover, and simmer, until the vegetables are falling apart, about 15 minutes.
Season to taste with salt and pepper, then swirl in the creme fraiche and heat until warmed through. Ladle the soup into bowls and garnish with the chives and a dollop of more creme fraiche if you like, and enjoy!