This soup is the splurge course. If you can't find truffle oil, drizzle extra-virgin olive oil over each serving.
Sort and rinse beans; place in a Dutch oven. Cover with water 2" above beans. Bring beans to a boil; cover, remove from heat, and let stand 1 hour. Drain beans; set aside.
Melt butter in Dutch oven over medium heat; add onion, celery, and garlic, and sauté 10 minutes or until golden. Add beans, chicken broth, bay leaves, and thyme; bring to boil. Reduce heat, and simmer, uncovered, 1 hour or until beans are tender, stirring occasionally. Remove from heat. Stir in vinegar and salt. Cool slightly. Remove and discard bay leaves.
Process 3 cups bean mixture in a blender until smooth, stopping to scrape down sides. Stir into remaining soup in Dutch oven. Spoon into soup bowls; top each serving with a Black Pepper Crouton, and drizzle with about 1 teaspoon truffle oil.
Christmas with Southern Living 2001