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.
We didn't have parsnips or celery on hand (so we used more carrot and potato), and we used vegetable broth instead of chicken, but we thought this was very tasty. The texture and color make it look unappetizing (so we may not serve it to company), but the taste is great!