How to Make It
Make the beans In a large saucepan, cover all of the ingredients with 4 quarts of water and bring to a boil. Simmer over moderately low heat until the beans are just tender, about 1 hour. Drain well and discard the vegetables.
Make the chili Season the pork and brisket generously with salt and pepper. In a large pot, heat the vegetable oil until shimmering. In batches, cook the pork and brisket over moderately high heat, turning occasionally, until browned all over, about 10 minutes per batch. Using a slotted spoon, transfer the meat to a baking sheet.
Add the onions, bell pepper, garlic and a generous pinch of salt to the pot. Cook over moderately high heat, stirring frequently, until just starting to soften and brown, about 5 minutes. Add the tomato paste, chili powder, brown sugar, mustard powder and cumin and cook, stirring, until fragrant and the vegetables are coated, about 3 minutes. Add the Hatch chiles and tomatoes and cook, stirring, until bubbling, about 5 minutes. Add the chicken stock and bring to a boil. Add the meat and oregano and simmer over moderate heat, stirring occasionally, until the meat is barely tender, about 1 hour.
Stir the beans into the chili and simmer over moderate heat, stirring occasionally, until the meat and beans are tender, about 1 hour and 15 minutes longer. Serve hot with sour cream, shredded cheese and thinly sliced scallions.