Season the pieces of beef generously with kosher salt and pepper (save the measured amounts of salt and pepper for the sauce).
Heat the 2 tablespoons of oil in a large skillet over medium-high heat. Sear the beef in a single layer — don't crowd the pan — for 5 minutes per side or until deeply browned. Work in batches. Transfer to the slow cooker.
Add the 4 chipotle peppers, 6 garlic cloves, 1/4 cup apple cider vinegar, 1/4 cup lime juice, 1 tablespoon cumin, 2 teaspoons oregano, 2 teaspoons kosher salt, 1 teaspoon cloves, and 1 teaspoon black pepper to a blender. Blend until smooth — this is your barbacoa sauce.
Pour the sauce over the seared beef in the slow cooker. Add the 1 cup beef broth and tuck the 3 bay leaves down into the liquid. The meat won't be submerged, that's okay.
Cover and cook on low for 8 hours, or until the connective tissue has broken down and the meat falls apart when pressed with a fork. Don't rush it — low heat over a long stretch is what gives you fall-apart tender barbacoa meat. Stir the meat a couple of times during cooking. Stir in cilantro when the meat is tender.
Transfer the beef to a baking dish or large bowl. Discard the bay leaves. Shred the meat with two forks, then ladle some of the cooking liquid back over the top of the meat to keep it juicy. Taste and adjust — an extra splash of apple cider vinegar or a squeeze of lime brightens it right up.
To make tacos: Warm the corn tortillas in a dry pan, 20 seconds per side. Pile on the shredded beef, then top with your favorite garnishes. Serve with Mexican rice and beans on the side.