Combine remaining ingredients (except for cornstarch and water) and pour over brisket. Cover and cook on LOW for 8 to 10 hours.
Remove meat from slow cooker and keep warm while you make a gravy. Pour the pan juices from the slow cooker into a saucepan and bring to a boil. In a small bowl, combine the cornstarch and water; slowly pour into the pan juices and whisk. Cook for about 2 minutes to thicken the sauce.