Preheat your oven to 300°F (150°C).
In a small bowl, mix together the brown sugar, smoked paprika, kosher salt, black pepper, and garlic powder.
Pat the brisket dry with paper towels, then rub the spice mixture evenly over all sides of the meat.
Place the seasoned brisket fat-side up in a large roasting pan or glass baking dish, then pour the beef broth into the bottom of the pan around the meat.
Cover the pan tightly with two layers of heavy-duty aluminum foil to seal in the steam. Bake for 3 hours.
Carefully remove the foil, brush the entire top and sides of the brisket generously with the barbecue sauce, and return it to the oven uncovered.
Bake uncovered for an additional 45 minutes until the sauce is bubbly, thick, and deeply caramelized.
Remove from the oven and let the brisket rest for 15 minutes before slicing against the grain.