How to Make It
Rinse the beans in a colander. In a large pot, bring 10 cups of water to a simmer over moderate heat. Add the rinsed beans, onions, garlic, carrots, oregano, cilantro and 1/2 teaspoon of salt. Reduce the heat to low and simmer partially covered, stirring occasionally, until the beans are tender, about 2 hours.
Discard the onion halves, carrots and herb stems. Season the beans with salt and pepper, and serve with tortillas, sour cream and lime wedges.