01 - Pat the brisket dry and season all sides with salt, black pepper, and smoked paprika.
02 - Layer sliced onions, carrot chunks, and celery chunks in the slow cooker; scatter minced garlic on top.
03 - Whisk together beef broth, barbecue sauce, tomato paste, Worcestershire sauce, brown sugar, dried thyme, and remaining smoked paprika in a bowl.
04 - Place the brisket atop the vegetables, pour the sauce evenly over it, then cover and cook on low for 8 hours until fork-tender.
05 - Transfer the brisket to a cutting board and allow it to rest for 10 minutes before slicing against the grain.
06 - Skim fat from the cooking juices, serve brisket with vegetables, drizzle with sauce, and garnish with parsley if desired.