01 - Rub kosher salt and black pepper evenly over all surfaces of the 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 - Arrange sliced onions, minced garlic, carrot pieces, and chopped celery around and beneath the brisket in the slow cooker.
04 - Whisk together beef broth, ketchup, Worcestershire sauce, brown sugar, apple cider vinegar, smoked paprika, and dried thyme in a bowl until sugar dissolves.
05 - Pour the sauce mixture evenly over the brisket and vegetables. Cover and cook on LOW setting for 8 hours until fork-tender.
06 - Remove brisket from slow cooker and let rest for 10 minutes. Slice across the grain into thin strips.
07 - Skim excess fat from cooking liquid if desired. Serve sliced brisket with vegetables and spoon sauce generously over the top.