Step 1: Pat the brisket dry thoroughly with paper towels. In a small bowl, combine all rub ingredients (brown sugar, smoked paprika, garlic powder, onion powder, chili powder, cumin, salt, black pepper).
Step 2: Generously rub the spice mixture all over the brisket, pressing it firmly into the meat.
Step 3: (Optional) Heat a large skillet or Dutch oven over medium-high heat with olive oil. Sear the brisket on all sides until nicely browned, about 2-3 minutes per side. This adds depth of flavor.
Step 4: Place the seared (or unseared) brisket into your slow cooker.
Step 5: In a separate bowl, whisk together the beef broth, Worcestershire sauce, apple cider vinegar, and liquid smoke (if using). Pour this mixture over and around the brisket in the slow cooker.
Step 6: Pour 1 cup of your chosen BBQ sauce over the brisket.
Step 7: Cover the slow cooker and cook on low for 8-10 hours, or on high for 4-6 hours, until the brisket is fork-tender and easily shreds apart.
Step 8: Carefully remove the brisket from the slow cooker and place it on a large cutting board. Use two forks to shred the brisket into desired pieces, discarding any large pieces of fat.
Step 9: Drain most of the liquid from the slow cooker, leaving about 1/2 to 1 cup of the flavorful juices. Return the shredded brisket to the slow cooker with the remaining liquid.
Step 10: Stir in the remaining 1 cup of BBQ sauce until the brisket is well coated. Let it warm through on the 'warm' setting or low for another 15-30 minutes, allowing the flavors to meld before serving.