01 - Pat the brisket dry with paper towels. Rub kosher salt and black pepper evenly over all surfaces of the meat.
02 - Heat a large skillet over medium-high heat. Sear the brisket for 3 to 4 minutes per side until deeply browned. Transfer the seared meat to the slow cooker.
03 - Arrange sliced onions, minced garlic, carrots, and celery underneath and around the brisket in the slow cooker insert.
04 - Whisk together beef broth, ketchup, Worcestershire sauce, brown sugar, apple cider vinegar, smoked paprika, and dried thyme in a medium bowl until the sugar dissolves completely.
05 - Pour the sauce mixture evenly over the brisket and vegetables. Cover with the lid and cook on LOW setting for 8 hours until the meat is fork-tender.
06 - Transfer the cooked brisket to a cutting board. Let rest for 10 minutes to allow juices to redistribute. Slice the meat against the grain into thin strips.
07 - Skim any excess fat from the cooking liquid. Serve sliced brisket with the cooked vegetables and ladle sauce generously over the top.