Black Bean, Sweet Potato, and Spinach Soup

I have no idea where I found this recipe but it is hearty and tasty.

1 tablespoon canola oil
1 yellow onion, chopped
3 sweet potatoes, peeled and cubed (about 1 3/4 pounds)
4 cups low-sodium vegetable broth
2 cups cooked or canned black beans, drained and rinsed
4 cups baby spinach leaves
1/4-1/2 cup low-fat sour cream
Salt, to taste

In a large saucepan, heat oil and sauté onion for 3 minutes until soft. Add sweet potatoes and stir to coat. Add broth. Bring to a boil, reduce heat, cover, and simmer for 15 minutes, until sweet potatoes are tender.

With a slotted spoon, scoop out 2 cups of sweet potato cubes; set aside. Puree remaining soup until smooth-I use an immersion blender. Return soup to pot, add remaining sweet potatoes and black beans, and cook for 5 minutes longer.

Stir in spinach and cook for 1 minute, until just wilted. Stir in sour cream and salt to taste. Serve hot. If you will not be serving all of it, Add a dollop of sour cream to individual bowls and not the entire pot.