In a large flat bottomed pan, fry the onions in little oil for 5-10 minutes or until they've begun to soften.
Add the garlic and dried spices and cook for a further 2-3 minutes.
Finally add the black beans to the pan and cook for another 5 minutes until all of the flavours have combined.
Transfer the beans, onions and spices to a blender and pour over the stock and the juice from the limes.
Blitz the mixture for 5 minutes or until completely smooth.
Transfer back to the pan and heat for another 5 minutes until the mixture has thickened.*
Before serving, stir in sour cream.
Serve with a sprig of fresh coriander!
* If you're making this soup in a Vitamix blender you can skip this step. Just make sure you've blended the mixture on the "Hot Soup" setting and you'll be able to enjoy the soup steaming hot straight out of the blender.