01 - Mix all spice rub ingredients in a small bowl. Pat brisket dry and rub spice mixture evenly over entire surface.
02 - Place sliced onions and smashed garlic in the bottom of a slow cooker. Lay the brisket on top, fat side up.
03 - Combine all BBQ sauce ingredients in a bowl and mix well. Pour half of the sauce over the brisket, reserving the other half.
04 - Pour beef broth around the brisket in the slow cooker, not directly over the meat.
05 - Cover and cook on low for 8 hours, or until the brisket is very tender and easily shreds with a fork.
06 - Carefully transfer cooked brisket to a cutting board. Let rest for 10 minutes, then slice or shred as desired.
07 - Skim excess fat from the cooking liquid and onions.
08 - Serve brisket with reserved BBQ sauce, either drizzled on top or on the side. Garnish with extra onions if desired.