The night before you plan to cook and serve the brisket, combine the salt, celery salt, garlic powder, onion powder and sugar in a small bowl and set aside. Place the brisket in a large roasting pan and trim the fat if it is super thick, but leave at least a ¼" layer on the bottom. Moisten the brisket with the Worcestershire sauce, then sprinkle the top and bottom of the brisket with half of the mixed seasonings, reserving the other half. Cover tightly with foil and place in the refrigerator overnight.

The next day, preheat the oven to 250 degrees. Remove the brisket from the fridge and uncover. Sprinkle it with the remaining seasonings, then cover it with foil again and place it in the oven to roast for 5 hours (approximately 1 hour per pound of meat).

Remove the brisket from the oven and remove the aluminum foil. Pour off the fat. In a medium bowl, stir together the brown sugar and barbecue sauce, then pour it over the brisket. Increase the oven temperature to 350 degrees, then return the brisket to the oven, uncovered, and roast an additional 30 minutes to an hour, or until the sauce is hot and the meat is tender. Slice or chop and serve.