01 - Pat the beef brisket dry with paper towels. Season generously on all sides with kosher salt and black pepper, pressing the seasoning into the meat.
02 - Heat a large skillet over medium-high heat. Sear the seasoned brisket for 3-4 minutes per side until a deep brown crust forms. Transfer to the slow cooker.
03 - Arrange the sliced onions, minced garlic, carrot pieces, and chopped celery in the bottom of the slow cooker. Place the seared brisket on top of the vegetable bed.
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 evenly over the brisket and vegetables. Cover and cook on LOW setting for 8 hours, or until meat reaches fork-tender consistency.
06 - Remove the brisket from the slow cooker and let rest on a cutting board for 10 minutes. Slice against the grain into thin strips.
07 - Skim excess fat from the cooking liquid if desired. Serve sliced brisket with vegetables and ladle sauce over portions.