Heat a cast-iron or stainless steel skillet over medium heat. Add the chiles and cook, turning occasionally, until lightly toasted and crispy. The chiles de arbol will take about 5 minutes; the anchos about  (Be careful not to inhale too deeply—chile smoke has been known to cause wild fits of coughing.) Discard the stems and seeds, and place the chiles in a clean coffee grinder or food processor. Grind into a fine dust. That's your chili powder—the heart of this dish. Heat the oil in a large pot over medium-high heat. Season the beef with salt and pepper, and add to the pan. Sear the meat until all sides are nicely browned, then add the onions, poblano peppers, garlic, cumin, and 2 tablespoons of the chili powder. Cook, stirring occasionally, for about 5 minutes, until the vegetables are softened. Stir in the tomatoes and stock. Lower the heat and simmer for at least 45 minutes (but preferably up to 90 minutes), until the beef is fork tender. Stir in the beans a few minutes before serving, and heat through. Serve with any of the garnishes.