Cook bacon in a Dutch oven over medium heat until crisp. Remove bacon from pan, reserving drippings in pan. Crumble bacon; set aside. Add leek and onion to pan; sauté 4 minutes. Add water, potato, lentils, carrot, salt, and broth; bring to a boil. Cover, reduce heat, and simmer 1 hour or until vegetables are tender. Place vegetable mixture in a blender or food processor; process until smooth. Return puréed mixture to pan; stir in half-and-half and sherry. Cook until thoroughly heated. Sprinkle with bacon.