Preheat the oven to 350 degrees F. Combine the chili powder, salt, garlic powder, onion powder, black pepper, sugar, mustard, and bay leaf in a small bowl. Mix well then rub onto all sides of the brisket. Place the brisket in a shallow roasting pan and place in the oven. Roast, uncovered, for 1 hour at 350 degrees F. Add the beef stock to the roasting pan. Add enough water to bring the liquid level up to 1/2-inch (if needed). Reduce the oven temperature to 300 degrees F. Cover the roasting pan tightly with aluminum foil. Place back in the oven and cook for 3 hours at 300 degrees F or until the brisket is tender. Remove from the oven and let sit, covered, for 5 minutes then slice the meat against the grain. Serve with the pan juices.