01 - In a small mixing bowl, combine ground cumin, dried oregano, smoked paprika, sea salt, black pepper, and cinnamon. Stir until evenly blended.
02 - Arrange the beef chuck pieces in the slow cooker. Sprinkle the spice blend generously over the meat and toss until every piece is thoroughly and evenly coated.
03 - Scatter the chopped onion, minced garlic, chipotle peppers, and jalapeño (if using) over and around the seasoned beef in the slow cooker.
04 - In a separate bowl, whisk together the fresh lime juice, apple cider vinegar, beef broth, and tomato paste until smooth. Pour the liquid evenly over the beef and aromatics.
05 - Tuck the bay leaves into the liquid around the beef to infuse flavor during cooking.
06 - Cover the slow cooker and cook on LOW for 8 hours, or until the beef is fall-apart tender and shreds effortlessly with minimal pressure.
07 - Discard the bay leaves. Using two forks, shred the beef directly in the slow cooker, allowing it to absorb and mix with the rich cooking juices.
08 - Serve the barbacoa hot in warm corn or flour tortillas, burritos, or over steamed rice. Garnish with fresh cilantro, diced onion, and lime wedges as desired.