01 - Pat the brisket dry with paper towels, then liberally season all surfaces with kosher salt and black pepper, pressing the spices into the meat to adhere.
02 - Heat a large skillet over medium-high heat until smoking hot. Sear the seasoned brisket for 3-4 minutes per side until a deep brown crust forms. Transfer the seared meat to a 6-quart or larger slow cooker.
03 - Distribute the sliced onions, minced garlic, carrot pieces, and celery chunks evenly around and underneath the brisket in the slow cooker insert, creating a flavorful roasting base.
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 brisket to a cutting board and allow it to rest for 10 minutes—this crucial step redistributes juices for maximum tenderness. Slice the meat against the grain into thin strips.
07 - Skim excess fat from the surface of the cooking liquid. Serve the sliced brisket alongside the tender vegetables, spooning the reduced sauce generously over each portion.