01 - Pat the beef brisket dry with paper towels, then rub kosher salt and black pepper evenly over all surfaces of the meat.
02 - Heat a large skillet over medium-high heat until smoking hot. Sear the brisket for 3 to 4 minutes on each side until a deep brown crust forms. Transfer the seared meat to the slow cooker.
03 - Arrange sliced onions, minced garlic, carrot pieces, and celery chunks in the bottom of the slow cooker, creating a bed for the brisket. Place the seared brisket 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 with the lid and cook on LOW setting for 8 hours until the meat is fork-tender and easily pulls apart.
06 - Carefully remove the brisket from the slow cooker and transfer 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 cooking liquid if desired. Serve sliced brisket alongside the cooked vegetables, spooning the sauce generously over the top.