01 - Pat the beef 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 until smoking hot. Sear the brisket for 3-4 minutes per side until a deep brown crust forms. Transfer the seared meat to the slow cooker insert.
03 - Scatter the sliced onions, minced garlic, carrot pieces, and chopped celery around and underneath the brisket in the slow cooker.
04 - Whisk together the beef broth, ketchup, Worcestershire sauce, brown sugar, apple cider vinegar, smoked paprika, and dried thyme in a 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 and easily shreds.
06 - Carefully transfer the brisket to a cutting board. Let it rest for 10 minutes to allow the juices to redistribute. Slice the meat against the grain into thin strips.
07 - Skim any excess fat from the surface of the cooking liquid. Serve the sliced brisket with the cooked vegetables. Spoon the sauce generously over the top.