Preheat your oven to 300°F.
In a small bowl, mix together the brown sugar, paprika, garlic powder, onion powder, black pepper, salt, and cayenne pepper (if using).
Rub the spice mixture all over the brisket, ensuring it is evenly coated.
Place the brisket in a large roasting pan, fat side up. Pour the beef broth around the brisket, being careful not to wash off the rub.
Cover the roasting pan tightly with aluminum foil and place it in the preheated oven. Roast for 4 to 5 hours, or until the brisket is tender and easily shreds with a fork.
Remove the brisket from the oven and let it rest for 20 minutes before slicing.
While the brisket is resting, increase the oven temperature to 400°F.
Slice the brisket against the grain and place the slices back in the roasting pan. Pour the barbecue sauce over the slices and return to the oven for an additional 15-20 minutes, uncovered, until the sauce is bubbly and caramelized.
Serve warm with your favorite sides.