My favourite Mexican restaurant used to serve a soup like this. Unfortunately it wasn't popular enough and it's disappeared off the menu. I found out how to make it myself though: I adapted a recipe from a Mexican cookbook and present the results to you here.

This soup is very easy to make although you need some time. Together with a salad and some bread (or tortilla chips!) it makes a meal by itself. This recipe makes for about 1.5l of soup, which should feed at least four people, or just you on four occasions. You will need:

Wash and sort the beans. Do not soak them! Put them into a large pan with the water and bring to a boil. Let simmer. Go do something else, this will take a while (two hours at the least, maybe three).

When the beans are almost soft, get out a frying pan, put it on the fire and pour in a bit of olive oil (the original recipe calls for lard, but olive oil is easier to obtain, better for your health, and suitable for vegetarians). Fry the cumin seeds until they start to smell and pop, then add chili pepper, onion and garlic and fry until they are soft. Finally add the tomato and oregano and let simmer for a few minutes. Add the mixture to the beans and cook until the beans are completely soft. Then puree the soup. Add the chopped cilantro and salt to taste.

When serving, add a dollop of sour cream to each bowl of soup.