Buttermilk Fennel Vichyssoise

Melt butter in a stockpot over medium-low heat. Add leek, season with salt, and cook, covered, until tender, about 15 minutes.

Add potatoes and stock. Bring to a boil, then reduce the heat and simmer until potatoes are tender, about 20 minutes. Stir in fennel (bulb and fronds) and cook for about 5-7 more minutes.

Working in batches, puree soup in a blender until smooth. Transfer pureed soup to a large bowl.

Season with salt and white pepper to taste. Stir in sour cream (or creme fraiche) and buttermilk just before serving. Adjust seasoning as needed. If necessary, thin the soup with a bit more chicken stock or water to achieve desired consistency.

Garnish, if you like, with a sliver of smoked salmon and a tiny drop of caviar. This soup may be served hot or cold.