Preparation In a large heavy saucepan cook diced fennel and onion in butter over moderate heat, stirring, until softened, about 10 minutes. Peel and cube potatoes. Add potatoes and broth to fennel mixture and simmer, covered, until potatoes are very tender, about 20 minutes. In a blender or food processor purée mixture in batches until smooth and return to saucepan. Stir in milk and salt and pepper to taste and simmer soup, stirring occasionally, 10 minutes, or until heated through. Garnish soup with reserved fennel leaves.
Preparation In a large heavy saucepan cook diced fennel and onion in butter over moderate heat, stirring, until softened, about 10 minutes. Peel and cube potatoes. Add potatoes and broth to fennel mixture and simmer, covered, until potatoes are very tender, about 20 minutes. In a blender or food processor purée mixture in batches until smooth and return to saucepan. Stir in milk and salt and pepper to taste and simmer soup, stirring occasionally, 10 minutes, or until heated through. Garnish soup with reserved fennel leaves.