Preheat the oven to 275 F.
Make sure that the meat is nice and clean , then pat dry it.
Do NOT remove all of ( if any) of the fat from the brisket.
Drizzle 2 tbsp of olive oil all over the brisket, and rub the oil all over the brisket.
Liberally sprinkle the barbecue rub all over the brisket, and massage it in.
Place all of the onions and peppers into a heavy roaster pan or dutch oven ( I used my dutch oven).
Next combine the beef broth and the liquid smoke , then pour it into the roaster or dutch oven.
Place the brisket on top of the onions and peppers( fatty part facing up), and then cover the roaster pan or dutch oven.
Let the brisket cook for 6 hours.
Remove the brisket from the oven, and uncover it, and place the brisket back into the oven, uncovered, for another 1 to 1 & 1/2 hours.
Remove the brisket from the oven, and let the meat rest for 20 minutes before cutting into it.