Stir together beef stock, soy sauce, lemon juice, garlic cloves, and hickory liquid smoke in a large roasting pan.
Place brisket in pan, fat side up. Spoon liquid over brisket.
Cover tightly with aluminum foil and chill 24 hours.
Preheat oven to 300°.
Bake brisket covered for approximately 40 minutes per pound. Test doneness by taking two forks and pulling gently on the meat. It should fall apart easily.
Uncover and let stand 20 minutes.
Place brisket on a cutting board. Trim fat by peeling it off the brisket with a fork.
Cut brisket across the grain into thin slices, or shred with two forks. Serve with pan drippings and mashed potatoes.