Heat oven to 325°F. Place ancho chilies and raisins in two separate small bowls. Cover both with hot water and let stand 20 minutes, or until softened. Drain, discarding liquid. Seed and stem the chilies.
Meanwhile, heat oil in a large Dutch oven over medium-high heat. Pat short ribs dry with paper towels and season with salt and pepper. Sear until well browned on all sides, about 15 minutes total.
While ribs are searing, prepare the braising sauce. Place garlic, onion, chicken stock, chipotle chilies, adobo sauce, and brown sugar in a food processor or blender, along with the soaked ancho chilies and raisins. Blend until sauce is mostly smooth (it should retain some texture). Stir in large pinches of salt and pepper; taste and adjust seasoning as needed.
After short ribs have browned, transfer to a plate. Pour the excess fat from the pan and discard. Add braising sauce, canned tomatoes, bay leaves, and cinnamon sticks. Simmer for 5 minutes. Return ribs to the pot, bring back to a simmer, cover, and place in the oven. Cook until ribs are tender and can be pulled apart with a fork, 2½ to 3 hours total. Remove from oven, spoon fat from the surface, and discard. Taste and adjust seasoning as needed. When cool enough to handle, shred meat with a fork and discard the bones.