Black Bean Soup with Sweet Potatoes

This recipe is from my friend Zsue. It's delicious!

2 tsp. canola oil
2 large onions finely chopped
1 T. ground coriander
1 T. ground cumin
5 (16 ounce) cans black beans, rinsed and drained
2 large sweet potato, peeled and chopped
6 fresh cilantro sprigs
1 tsp. salt
1 tsp. freshly ground pepper
2 qts. vegetable broth (or chicken, or beef)
¼ c. plain low-fat yogurt for garnish
4 thin lime slices finely chopped, for garnish
Fresh cilantro leaves, for garnish

1. Heat oil in a large skillet over medium heat. Add onion and cook, stirring occasionally, until softened, about 5 minutes. Add the coriander and cumin; cook stirring constantly, until fragrant about 30 seconds.

2. Place 4 cans of beans in a 5 or 6 qt. slow cooker. Add the onion mixture, potato, cilantro sprigs, salt and pepper. Pour the broth over the beans and vegetables. Cover and cook until the vegetables are fork tender, 4-5 hours on high or 8-10 hours on low. Discard the cilantro sprigs.

3. Pour the soup in batches into a blender or food processor and puree. Return the soup to the slow cooker. Add the last can of whole beans to soup. Garnish each serving with the yogurt, lime slices and cilantro leaves.