Heat olive oil in a large Dutch oven over medium-high heat. Add potato, carrot, celery, parsnip, and shallots to pan; sauté for 7 minutes or until tender. Add sherry vinegar to pan, scraping pan to loosen browned bits. Add chicken broth, lentils, and bay leaves to pan; bring to a boil. Reduce heat, and simmer 45 minutes or until lentils are tender. Discard bay leaves.
Transfer half of lentil mixture to a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth, scraping sides. Return lentil mixture to pan; stir in pepper and salt.