Day 1: Sprinkle both sides of the brisket with garlic powder, onion powder, and celery salt. Place in a marinating dish, or a bag, or a Foodsaver marinating canister, and sprinkle with liquid smoke. This is a liquid sold under several different brand names. The one I have is called Wright's Hickory Seasoning Liquid Smoke, and comes in a 3.5 oz. bottle. Use about a third of the bottle for a 1.5 pound brisket, two thirds for a 3 pound brisket, and the whole bottle if you're doing a huge cut of meat. Seal bag or canister and marinate in the refrigerator at least overnight.
Day 2, early morning: Sprinkle brisket generously with Wocestershire sauce. For my 1.5 pound brisket, which is a small one, I used about 3 tablespoons. Place in a baking dish and cover with foil. Bake for four hours at 275˚. Remove from oven, let cool for about an hour, and then place, still covered, in the refrigerator.
Day 2, 45 minutes before you want to eat: Remove brisket from pan and put on cutting board; slice thinly across the grain. It will seem tough, but it softens to a wonderful tenderness when it's reheated. Lift congealed grease from baking dish and discard. Put meat back in pan, and cover with about 1 cup of prepared barbecue sauce. I use either Bullseye or K.C. Masterpiece, since they don't have that raw sour taste that Kraft and Hunt's do. It's up to you.
Cover dish again with foil and bake at 325˚ for about 30-35 minutes. Enjoy!