01 - Pat the brisket dry with paper towels. Combine smoked paprika, garlic powder, onion powder, ground cumin, dried thyme, chili powder, salt, and black pepper in a bowl. Rub evenly over the brisket.
02 - Scatter sliced onion and minced garlic at the bottom of the slow cooker. Place the seasoned brisket on top.
03 - Whisk together ketchup, apple cider vinegar, brown sugar, Worcestershire sauce, Dijon mustard, smoked paprika, garlic powder, cayenne pepper, and salt in a medium bowl. Pour half the sauce over the brisket; reserve remaining sauce for serving.
04 - Pour beef stock around the brisket in the slow cooker, avoiding pouring over the meat.
05 - Cover and cook on low heat for 8 hours until brisket is tender and easily shredded with a fork.
06 - Remove brisket carefully and let it rest for 10 minutes. Slice or shred to preference.
07 - Skim excess fat from cooking juices. Optionally simmer juices in a saucepan to thicken and concentrate flavors.
08 - Serve the brisket with reserved BBQ sauce and reduced cooking juices as desired.