Preheat the oven to 350 degrees.
In a medium bowl, pour boiling water over the ancho chiles to rehydrate them. If they float to the surface, use a small bowl to submerge them. Set aside.
In a large oven-proof Dutch oven, heat 1-2 tablespoons of olive oil over medium-high heat. Saute the bacon until browned all over. Turn the heat down to medium, add the onions and continue to sauté until tender. Stir in the beef and return the heat to high.
While the beef cooks, at the garlic, ancho chiles, chipotle chiles, and 1 cup of the soaking liquid to a small food processor. Blend until smooth.
To the pot, add the chili mixture and the spices (chili powder, cumin, oregano, coriander, salt) and toss to coat. Cook for a few minutes until very fragrant, and then add the beer, green chiles, 2 cans of tomatoes, and cilantro stems. Bring the chili to simmer.
Cover the pot and place it in oven. Cook 2 hours. Uncover and cook until beef is almost tender, about 1 hour. Stir in the pumpkin, and the remaining can of tomatoes and return to the oven. Cook uncovered until beef and pumpkin are tender, about 1 hour longer. Tilt pot and spoon off any fat from surface of sauce.
Taste for seasoning, and serve with a dollop of sour cream, a slice of avocado, and a sprinkle of cheese.