01 - Pat the brisket dry with paper towels. Combine all spice rub ingredients in a small bowl and rub evenly over the brisket.
02 - Layer the sliced onion and minced garlic in the base of the slow cooker. Place the brisket on top.
03 - Whisk all BBQ sauce ingredients in a medium bowl. Pour half over the brisket; reserve the remainder for serving.
04 - Pour beef stock around the brisket within the slow cooker without pouring it directly over the meat.
05 - Cover and cook on low for 8 hours until the brisket is tender and can be shredded easily with a fork.
06 - Remove the brisket carefully and let it rest for 10 minutes before slicing or shredding as preferred.
07 - Skim off excess fat from the cooking liquid. Optionally, reduce the cooking juices in a saucepan to thicken.
08 - Serve the sliced brisket with reserved BBQ sauce and reduced cooking juices if desired.