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 on each side until a deep brown crust forms. Transfer the seared meat to the slow cooker.
03 - Arrange 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 - In a medium bowl, whisk together beef broth, ketchup, Worcestershire sauce, brown sugar, apple cider vinegar, smoked paprika, and dried thyme 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 offers no resistance when pierced with a fork.
06 - Transfer the cooked brisket to a cutting board. Let it rest for 10 minutes to allow the juices to redistribute. Slice the meat crosswise against the grain into thin strips.
07 - Skim any excess fat from the surface of the cooking liquid. Serve the sliced brisket alongside the tender vegetables, spooning the warmed sauce generously over each portion.