Make sure the dried fava beans are clean and free of dirt. Place in a large soup pot and cover with the broth. Simmer over medium-low heat, partially covered, until very tender, about an hour. The beans should be starting to fall apart at this point. While the beans are simmering, roast the garlic in a heavy skillet over medium heat, turning occasionally, until you get black spots all over, and the cloves have softened up - about 15 minutes. Cool a bit, remove the papery skins, chop finely and set aside. Now, you'll want to caramelize the onions a bit as well. I used my broiler, but you could also do it in a dry skillet or on a grill. In this case I placed the onions in a single layer, on a rimmed baking sheet, about 4-inches / 10cm under a hot broiler for 4-5 minutes on each side, until soft and deeply browned. Cool a bit, peel and finely chop. Use the same pan under a hot broiler to roast the tomatoes until blackened on one side, six minutes or so. Flip, and roast the other side, another 6 minutes. Cool a bit, then peel and chop, saving all the juices. Add the garlic, onion, and tomatoes to the fava beans and simmer until the beans are the consistency of a coarse puree, 15-30 minutes. While the soup is simmering, cut the chiles into confetti-shaped flecks using scissors or a sharp knife. Heat the oil in a small saucepan over medium heat. Add the chiles and stir for a minute, then remove from the heat. Add the vinegar, 3 tablespoons of water, oregano, and 1/2 teaspoon of the salt. Set aside and let stand for at least 1/2 hour, stirring occasionally. Just before serving, add enough water, if necessary, to bring the soup to the consistency of a medium-thick bean soup. Let the soup come back up to a simmer, remove from heat, then stir in the mint, cilantro, and another teaspoon of salt. Taste, and add more salt if needed, but keep in mind the cheese is salty as well. Serve with a dollop of the chile mixture, sprinkled with a bit of the cheese. Serves 8 to 10. Adapted from the Slow-Simmered Fava Bean Soup with Mint and Pasilla Chile recipe in Rick Bayless's Mexican Kitchen .
