Place beef brisket, fat side up, in 13 x 10 inch shallow roasting pan. Sprinkle brisket evenly with salt, pepper and garlic. Top with onion.
Bake in 350°F oven 1 hour, or until onions turn brown.
Add 1 cup hot water and cover pan tightly with aluminum foil.
Reduce oven temperature to 300°F and continue cooking 2 hours or until brisket is tender.
Remove brisket and onions to warm platter. Skim fat from juices or use a gravy separator.
To make gravy, combine 1 cup water and cornstarch. Add to juices in pan. Cook over medium heat, stirring constantly, until gravy boils and thickens.
Carve brisket across the grain into thin slices.
Serve brisket and onions with gravy.
SOURCE: The Texas Beef Council