01 - Pat the beef brisket dry with paper towels. Generously season all sides with kosher salt and black pepper, pressing the spices into the meat.
02 - Heat a large skillet over medium-high heat until smoking hot. Sear the seasoned brisket for 3 to 4 minutes per side until a deep brown crust forms. Transfer the seared meat to the slow cooker.
03 - Arrange the sliced onions, minced garlic, carrot pieces, and chopped celery in an even layer at the bottom of the slow cooker. Place the seared brisket on top of the vegetable bed.
04 - Whisk together the 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, or until the meat offers no resistance when pierced with a fork.
06 - Carefully transfer the cooked brisket to a cutting board. Let it rest for 10 minutes to allow the juices to redistribute. Slice the meat across 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 warm sauce generously over each portion.