Black Bean and Sweet Potato Soup

I've had this soup stuck in my head for weeks, but lost the recipe. I re-found it in an old issue of Fine Cooking on Saturday morning and got straight to making it.

Black Bean and Sweet Potato Soup
modified from Fine Cooking, January 2009
Makes 14 cups, about 8 servings

2 T oil
2 onions, chopped
3 cloves garlic, chopped
1 1/2 tsp ground coriander
1 tsp ground cumin
1/4 tsp black pepper
2 quarts chicken or vegetable stock
6 cups cooked black beans*
2 sweet potatoes, peeled and cut into 1/2 inch cubes
3/4 tsp salt


Saute the onions over medium heat in a large pot. Cook until starting to soften and brown slightly, about 8 minutes.

Add the garlic, coriander, cumin, pepper, and cook, stirring constantly, until fragrant, about 30 second.

Add the broth beans, sweet potatoes, salt and bring to a boil over high heat. Reduce the heat and simmer until sweet potatoes are tender, at least 15 minutes. I simmered for at least 30 minutes, it might have been closer to an hour because I really wanted the flavors to blend.

Puree 3/4 of the soup, leaving the remainder chunky. Season to taste with salt and pepper. Served topped with a dollop of yogurt and a slice of lime**.

Notes:
* 6 cups of cooked black beans = four 15.5 oz cans OR 2 cups dried beans
** The original recipe called for plain yogurt, but I used a toasted cumin yogurt recipe from smitten kitchen and it was awesome! See the original recipe at
http://smittenkitchen.com/2010/01/black-bean-soup-toasted-cumin-seed-crema/
Take 1 Tablespoon cumin seeds and toast them in a dry pan on the stove for about 60 seconds until they start to brown. Grind them up and mix them into 1 cup yogurt, sour cream or creme fraiche. I used greek yogurt.
** I didn't have any limes, but I bet a squeeze of fresh lime juice would be really good. Rob was wishing for more spice, but I really like that you can taste the sweet potato. I suppose you could add some cayenne pepper or jalapenos.