01 - Pat the brisket dry with paper towels, then generously season 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 the seared meat to the slow cooker insert.
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 directly on top of the vegetables.
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 sauce mixture evenly over the brisket and vegetables. Cover the slow cooker with its lid. Cook on LOW setting for 8 hours until the meat is fork-tender and easily shreds.
06 - Carefully transfer the cooked brisket to a cutting board. Let the meat rest for 10 minutes to allow juices to redistribute. Slice the brisket 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 reduced cooking sauce generously over each portion.