Lightly grease your slow cooker and place brisket inside. Whisk together sauce ingredients (except cold water + corn starch) in a small bowl, set aside.
Stir together seasonings and rub all over brisket. Pour sauce over brisket, cover and cook on low for 10 hours.
Pour liquid from the slow cooker into a large sauce pan. Bring to a boil over medium-high heat. Stir cornstarch into cold water until dissolved, then pour into sauce pan. Reduce heat to medium-low and stir until sauce is thickened. Remove from heat.
Shred beef with two forks and pour sauce back into the slow cooker, give it a good stir and serve hot.
Notes
Sauce can be made in advance and stored in fridge until ready to use.