El Torito's Black Bean Soup

12 oz. dried black beans
8 cups chicken or vegetable stock
2 teaspoons olive oil
1 onion, chopped
1 cup carrots, chopped
1 cup celery, chopped
2 cloves garlic, minced
2 teaspoons dried oregano
1 teaspoon dried thyme
1 bay leaf
1/2 teaspoon cayenne pepper
3 tablespoons fresh lime juice
Fresh cilantro (optional)

Rinse and sort though black beans, discarding any that are shriveled or discolored. Place beans in a large stockpot. Cover beans with water and refrigerate to soak overnight. Drain beans and return to stockpot. Add stock and heat to boiling. Meanwhile, heat olive oil over medium-high heat in a large skillet. Add onion, carrot, celery and garlic and saute until tender, approximately 5 minutes. Add to stockpot along with oregano, thyme, bay leaf and cayenne pepper. Cover stockpot and reduce heat to simmer for 3 to 4 hours. Transfer soup to blender or food processor and puree to desired thickness. Just before serving add lime juice and garnish with a sprig of fresh cilantro, if desired.
Add salt and pepper to taste and serve.