1. Heat the oil in a large heavy-bottomed pot over medium-high heat and sweat the leeks and fennel, stirring, for about 2 minutes. Add the garlic and cook 2 minutes more. 2. add the potatoes, chicken broth and cream. Bring to a boil, then reduce immediately to a simmer. Cook until the potatoes are soft, about 20 minutes. 3. Transfer the soup to a blender and puree. Season with salt and pepper. Garnish with chopped fennel fronds.