Sort and wash beans; place in a large bowl. Cover with water to 2 inches above beans; cover and let stand 8 hours. Drain.
Combine beans, broth, and next 5 ingredients (through chile) in an electric slow cooker. Cover and cook on LOW 10 hours. Discard bay leaves. Stir in juice and salt. Ladle 1 1/2 cups soup into each of 6 bowls; sprinkle each with 2 teaspoons chopped cilantro. Top each serving with 1 1/2 teaspoons sour cream. Garnish with cilantro sprigs, if desired.
This recipe has been retested for Cooking Light Slow Cooker Tonight, 2012
I think quality ingredients are key for this recipe. I use cumin so frequently that I always have a fresh bottle on hand. Fresh vibrant cilantro is also key. I also highly recommend braising the onions along with a boneless skinless pork chop. These additions to the recipe are a simple way of raising the flavor profile without adding to the calories significantly.
I make this using all chicken stock, rather than the water and vegetable broth, and I puree the whole soup - with the cilantro - when it's finished. Then I stir in the lime at the end. When I do this, the soup comes out creamy, thick, and flavorful. We add the sour cream dolloped on top at the end, and my whole family loves it. Actually, my family adds the sour cream, but I add plain yogurt because I like the slightly sour taste it adds. I feel it complements the lime well. I serve it with warmed corn tortillas or corn bread and a salad. Very easy, and the house smells great when I come home to it.