Liberally salt and pepper the brisket
Whisk together the beef broth, liquid smoke, worcestershire sauce, garlic powder, and onion powder for the marinade
Add the marinade to a large resealable plastic bag
Add the brisket, squeeze out the excess air, and seal the bag
Refrigerate for 24 hours, turning the bag over a few times to make sure the brisket is evenly marinated
Preheat the oven to 275 degrees
In a large baking dish, pour in the beer and add the chopped garlic and the sliced onion
Remove the brisket from the marinade and add to the baking dish
Discard the marinade
Cover with aluminum foil
Bake for 6 hours
Remove the brisket from the baking dish, cover and let rest 15 minutes
Slice against the grain and brush with bbq sauce