01 - Pat the brisket dry and season generously on all sides with salt, pepper, smoked paprika, thyme, and cumin.
02 - Heat olive oil in a large skillet over medium-high heat. Sear the brisket 3 to 4 minutes per side until deeply browned. Transfer to a plate.
03 - In the same skillet, cook sliced onions for 5 to 7 minutes, stirring occasionally, until softened and starting to caramelize. Add minced garlic and cook another minute.
04 - Layer half the onions in the bottom of the slow cooker. Place the seared brisket on top, then cover with remaining onions.
05 - Pour beef broth, red wine (if using), and Worcestershire sauce evenly over the brisket and onions.
06 - Cover and cook on low heat for 6 to 8 hours until the brisket is fork-tender.
07 - Transfer brisket to a cutting board. Let rest for 10 minutes, then slice against the grain.
08 - Skim excess fat from cooking liquid. Serve brisket slices topped with onions and spoonfuls of pan juices.