Trim the green portions of the leek and, using 2 of the largest and longest leaves, make a bouquet garni by folding the 2 leaves around the bay leaves, peppercorns and thyme. Tie into a package-shaped bundle with kitchen twine and set aside. (Alternately, tie 2 leek leaves, bay leaves, peppercorns and thyme together in a piece of cheesecloth.)

Using a sharp knife, halve the white part of the leek lengthwise and rinse well under cold running water to rid the leek of any sand. Slice thinly crosswise and set aside.

In a large soup pot over medium heat, melt the butter and add the bacon. Cook for 5 to 6 minutes, stirring occasionally, until the bacon is very soft and has rendered most of its fat. Add the chopped leeks and cook until wilted, about 5 minutes. Add the wine and bring to a boil. Add the reserved bouquet garni, chicken stock, potatoes, salt and white pepper, and bring to a boil. Reduce the heat to a simmer and cook for 30 minutes, or until the potatoes are falling apart and the soup is very flavorful.

Remove the bouquet garni and, working in batches, puree the soup in a food processor or blender. (Alternately, if you own an immersion blender, puree the soup directly in the pot.) Stir in the creme fraiche and adjust the seasoning, if necessary. Serve immediately, with some of the snipped chives sprinkled over the top of each bowl of soup.