Cut brisket in half; rub with liquid smoke, if desired, and celery salt, pepper and salt. Place in a 3-qt. slow cooker. Top with onion. Combine beer and Worcestershire sauce; pour over meat. Cover and cook on low for 8-9 hours or until tender.
Remove brisket and keep warm. Strain cooking juices; transfer to a small saucepan. In a small bowl, combine cornstarch and water until smooth; stir into juices. Bring to a boil; cook and stir until thickened, about 2 minutes. Serve beef with gravy.

Test Kitchen tips
This is a fresh beef brisket, not corned beef.
The addition of liquid smoke will give a depth of flavor to this recipe. Be careful not to overdo it; a small amount goes a long way.