Trim off the tough upper green part of the leeks and the root ends and discard. Slice the leeks in half and thinly slice into half-moons. Rinse in a bowl of cold water to get all the dirt off the leeks. Lift the leeks out of the cold water and let drain.
Peel the potatoes cut them in half, and then slice into thin half-moons. Place a medium soup pot over medium heat. Melt the butter and add the leeks, thyme, bay leaf, some sea salt, and black pepper. Stir to coat the leeks and cook on medium-low heat until soft, about 7-10 minutes. Do not brown. Add the potatoes and cook for another couple of minutes, stirring to coat them as well.
Next, add the chicken stock. Bring the mixture to a boil and then reduce the heat to a simmer.
Cook for 25-30 minutes or until the potatoes are tender. At this stage, you have two choices. You can leave it as a chunky soup or you can puree it to get a smoother, creamier soup. Both are delicious. Either way, remove the thyme and bay leaf. Taste and season your soup. If pureeing, use an immersion blender or a blender, but be careful when blending hot soup in a blender, as you must allow heat to release from the top or it will explode. If the soup is too thick, you can thin it out with extra broth.
Garnish your soup with a dollop of creme fraiche, minced chives, black pepper, and some extra virgin olive oil.