Rinse lentils and set them aside.
To a large dutch oven, add olive oil, butter, onions, celery, carrots, and garlic. Cook over medium/high heat until vegetables are soft.
Add stock, lentils, and bay leaf. Bring to a boil. Cover and cook over low heat for an hour or until lentils are tender.
Cut sausage (if desired) and stir into soup. Add in wine, chopped parsley, and salt & pepper to taste. Cook for an additional 10-15 minutes uncovered to allow sausage to cook and flavor the soup.