01 - Rub the brisket generously with kosher salt and freshly ground black pepper, coating all sides evenly.
02 - Arrange the sliced onions and minced garlic in an even layer at the bottom of the slow cooker insert.
03 - In a medium bowl, whisk together ketchup, apple cider vinegar, brown sugar, Worcestershire sauce, Dijon mustard, smoked paprika, garlic powder, onion powder, and cayenne pepper until smooth and fully combined.
04 - Place the seasoned brisket on top of the onion bed, fat side facing up.
05 - Pour the prepared BBQ sauce evenly over the brisket, ensuring the meat is completely coated.
06 - Cover with the lid and cook on low setting for 8 hours until the meat is fork-tender and easily pulls apart.
07 - Carefully transfer the brisket to a cutting board and let it rest for 10 minutes before slicing.
08 - Skim any excess fat from the cooking liquid. For a thicker consistency, transfer the sauce to a saucepan and simmer for 10 minutes to reduce.
09 - Slice the brisket against the grain into thin strips. Serve warm, spooning the reduced BBQ sauce over the top.