Place the sliced onion at the bottom of the slow cooker.Add the beef chunks on top of the onions.
For the Adobo Sauce: in a blender blend the chipotles, garlic, lime juice, apple cider vinegar, cumin, oregano, salt, pepper, and nutmeg with the beef stock until smooth.
Pour the blended adobo sauce over the crockpot contents, ensuring each piece is well coated. Use tongs for an even coat.
Tuck the bay leaves into the mix, cover, and set your slow cooker on low for 8-9 hours or high for 4-5 hours. Wait for the magic to happen — the beef should be tender enough to fall apart easily.
Once cooked, remove the beef from the slow cooker and shred it using two forks.
Return the shredded beef to the slow cooker, mixing it into the sauce to soak up all that flavorful goodness.
Serve your barbacoa over a bed of cauliflower rice, topped with your favorite garnishes like guac, pico de gallo, roasted peppers and onions, and salsa. Because we all deserve the good stuff. Or serve on tortillas and make it taco night.