01 - Preheat your oven or smoker to 275°F (135°C).
02 - In a small bowl, combine kosher salt, black pepper, smoked paprika, garlic powder, onion powder, ground cumin, dried oregano, and Carolina Reaper chili powder.
03 - Thoroughly rub the spice blend over all surfaces of the brisket.
04 - Place the seasoned brisket in a large roasting pan or disposable foil tray, ensuring the fat side is facing up. Scatter sliced onion and smashed garlic cloves around the meat.
05 - In a separate bowl, whisk together beef broth, apple cider vinegar, Worcestershire sauce, brown sugar, tomato paste, and Dijon mustard. Pour this mixture around the brisket in the pan.
06 - Cover the pan tightly with aluminum foil or a lid. Cook in the preheated oven or smoker for 4 hours.
07 - Uncover the brisket. Baste with some of the accumulated cooking juices. Increase the oven or smoker temperature to 325°F (160°C). Cook uncovered for an additional 45–60 minutes, basting once more, until the brisket is deeply browned and yields to tender pressure (internal temperature approximately 200°F / 93°C).
08 - Remove the brisket from the heat and let it rest, tented loosely with aluminum foil, for 20 minutes. This allows the juices to redistribute.
09 - Slice the rested brisket against the grain. Serve with the pan juices spooned over the top.