01 - Rub kosher salt and black pepper evenly over all surfaces of the trimmed beef brisket.
02 - Heat a large skillet over medium-high heat. Sear brisket for 3-4 minutes per side until deeply browned. Transfer to slow cooker.
03 - Place sliced onions, minced garlic, carrots, and celery in the bottom of the slow cooker, creating a bed for the meat.
04 - Whisk together beef broth, ketchup, Worcestershire sauce, brown sugar, apple cider vinegar, smoked paprika, and dried thyme until sugar dissolves.
05 - Pour sauce over brisket and vegetables. Cover and cook on LOW setting for 8 hours until meat is fork-tender.
06 - Transfer brisket to cutting board. Let rest 10 minutes before slicing against the grain into thin strips.
07 - Skim excess fat from cooking liquid. Serve brisket slices with vegetables and spoon sauce over top.