In a Dutch oven, sweat the onions, garlic, chiles, cilantro, annatto seed paste, chili powder, cinnamon, oregano, and cumin in the olive oil. Add the lamb stew meat, and continue to cook until the meat has caramelized just slightly. Deglaze with the beer. Add the lamb stock, and tomatoes. Put the lid on and pop it into the oven while the shearing goes on. Stir it occasionally and cook for about 4 to 6 hours. When the shearing is done, grate the chocolate into the chili, which by now should be sublime. Ladle it into bowls and top it with the grated Cotija cheese and serve with a nice cold beer, fresh cornbread, a salad and feel the flavors of Mexico transport you!