Heat olive oil in a large Dutch oven over medium-high heat.
Add potato, carrot, celery, parsnip, and shallots to pan; saut 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.