Marinate brisket in a mixture of the onion, garlic and celery salts and liquid smoke. Rub in well and poke holes in meat to help tenderize it. Marinate overnight or at least 3 hours.
Make a pouch of aluminum foil. Put meat in it and add salt and pepper to taste and Worcestershire sauce. Seal pouch well and bake at 275° F for 4 to 6 hours.
Open pouch and put onion soup mix and small bottle of barbecue sauce over brisket. Seal pouch again and bake 1 hour longer.
Refrigerate for 1 hour before slicing across grain. After slicing, reheat in foil.
Servings: