Black Bean Soup

I prefer soups for lunch both during winter and summer. During summer, this helps us not to feel so thirsty, as with some other foods; and during winters, the warmth that a hot bowl of soup provides is unparalleled.  The black bean soup is one of my all time favorites as this is easy on your stomach yet filling enough. I got this recipe from Jay's cousin, when she threw a soup party. And ever since, this had been a staple at our house.
Adapted from How to Cook Everything by Mark Bittman - serves 4-6

Ingredients

3 tablespoons canola or olive oil
2 medium onions, chopped
2 cloves garlic, minced
1 1/2 tablespoons chili powder, or more to taste
2 15-ounce cans black beans, or 3 cups cooked from dry
4 cups chicken or vegetable stock
Juice of 1 lime, or to taste
2 Carrots
1/2 cup chopped Cilantro
1 green chilli
Sour cream or plain yogurt to garnish, or 1 egg
1/4 cup cilantro, chopped
Method:
Heat 2 tablespoons of the oil in a heavy soup pot over medium heat. Add the onions and cook until softened, about 5 minutes. Stir in the garlic green chilies, coriander leaves, and carrots and chili powder and cook, stirring constantly, for an additional minute.
Add the beans, stock, and salt and pepper to taste. Bring to a gentle boil, then simmer, stirring occasionally, for 15-20 minutes.
If using the egg, heat an additional tablespoon of oil in a non-stick skillet over medium-low heat in the meantime. Add the egg, cover, and fry slowly until the whites are completely set and the yolk is to your liking (I prefer it soft so it disperses into the soup).
To thicken the soup, purée it briefly with a stick blender, transfer half through food mill or into a blender, or just mash it by hand. Remove from the heat and add the lime juice. Adjust seasoning as necessary, garnish with cilantro and egg or yogurt or sour cream. Serve hot.