01 - Pat the brisket dry with paper towels. Season generously on all sides with kosher salt and black pepper, pressing the seasoning into the meat.
02 - Heat a large skillet over medium-high heat until smoking hot. Sear the brisket for 3 to 4 minutes per side until a deep brown crust forms. Transfer to the slow cooker.
03 - Arrange the sliced onions, minced garlic, carrot pieces, and chopped celery in the bottom of the slow cooker. Place the seared brisket directly on top of the vegetables.
04 - 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 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 pulls apart.
06 - Transfer the brisket to a cutting board and let rest for 10 minutes. Slice the meat against the grain into thin strips for maximum tenderness.
07 - Skim any excess fat from the cooking juices. Serve the sliced brisket alongside the tender vegetables, spooning the sauce generously over the top.