Crumble sausage in a Dutch oven; add onion, carrot, celery, and garlic. Cook over medium-high heat 5 minutes or until sausage is browned and vegetables are tender, stirring frequently. Add 2 cans black beans, chicken broth, and next 7 ingredients.
Place remaining 1 can black beans in a bowl; mash with a fork, and add to soup mixture. Bring to a boil; reduce heat, and simmer, uncovered, 30 minutes or until thickened. Ladle soup into individual bowls. Top each serving with 1 tablespoon sour cream. Garnish with fresh cilantro leaves, if desired.