01 - Pat the beef dry and evenly season with salt, pepper, smoked paprika, cumin, and chili powder.
02 - Heat olive oil in a large skillet over medium-high heat and sear the beef on all sides until deep brown, about 3 to 4 minutes per side.
03 - Place sliced onions and minced garlic into the slow cooker, then set the seared beef on top.
04 - Whisk together beef broth, barbecue sauce, apple cider vinegar, Worcestershire sauce, and brown sugar. Pour the mixture over the beef.
05 - Cover and cook on low for 8 hours until beef is tender enough to shred easily.
06 - Remove beef from slow cooker and shred using two forks. Return shredded beef to the cooker and combine with cooking juices.
07 - In a large bowl, whisk mayonnaise, apple cider vinegar, Dijon mustard, honey, celery seed, salt, and pepper. Toss shredded cabbage and carrots with the dressing. Refrigerate until serving.
08 - Pile shredded beef onto buns, drizzle with extra barbecue sauce if desired, then top with slaw. Serve immediately.