Season the beef with salt, pepper, and cumin. Sear in a skillet on all sides until browned, about 5-7 minutes.
In a blender, combine garlic, onion, ancho chili peppers, chipotle peppers, cumin, oregano, cloves, beef broth, vinegar, and lime juice. Blend until smooth.
Place the seared beef into the slow cooker and pour the blended sauce over it. Add bay leaves. Cook on low for 8 hours or on high for 4 hours.
Once the beef is tender, remove it and shred with a fork. Return the shredded beef to the slow cooker to soak up the juices.
Taste and adjust seasoning with salt or lime juice if needed. Serve the beef barbacoa in tacos, burritos, or bowls.
Notes
Feel free to adjust the level of heat in your barbacoa by adding more or fewer chipotle peppers. This recipe also works great with different cuts of beef like brisket or short ribs.