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 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 around and underneath the brisket in the slow cooker insert.
04 - In a medium bowl, whisk together the beef broth, ketchup, Worcestershire sauce, brown sugar, apple cider vinegar, smoked paprika, and dried thyme until the sugar dissolves completely.
05 - Pour the prepared sauce evenly over the brisket and vegetables, ensuring some liquid reaches the bottom of the cooker.
06 - Cover the slow cooker with its lid. Cook on LOW setting for 8 hours until the brisket is fork-tender and easily shreds.
07 - Carefully transfer the brisket to a cutting board. Let it rest for 10 minutes to allow juices to redistribute. Slice the meat against the grain into thin strips.
08 - Skim any excess fat from the surface of the cooking liquid. Serve the sliced brisket alongside the cooked vegetables. Spoon the remaining sauce over the meat before serving.