Brush entire brisket with liquid smoke. Sprinkle with meat tenderizer and celery seeds. Wrap in heavy-duty foil, sealing well to keep juices in. Place on baking sheet with edges and bake at 250° F for 7 hours.
Remove from oven. Drain any drippings from pan and carefully drain drippings from inside foil wrapping to measure 3/4 cup. Remove foil from brisket; cool and refrigerate overnight.
To serve, thinly slice the meat and place in a 9x13-inch pan. Combine reserved drippings, barbecue sauce, ketchup and brown sugar, blending well. Pour over brisket. Cover and heat at 325° F for 1 hour.
Servings: 14 to 16