Chinese Pot Roast

Combine first 4 ingredients; stir well. Rub garlic mixture over entire surface of roast. Place roast in an ungreased 13 x 9 x 2-inch dish. Combine soy sauce, brown sugar, and sherry; pour marinade mixture over roast. Cover and marinate refrigerator 30 minutes, turning once. Remove roast from marinade, reserving marinade. Brown roast in oil in a large Dutch oven over medium heat. Pour reserved marinade and 1 1/2 cups water over roast. Bring to a boil; cover, reduce heat, and simmer 2 hours. Add potato, carrot, celery, and onion. Cook an additional 30 minutes or until vegetables are tender. Remove roast and vegetables to a serving platter, reserving pan juices. Set roast and vegetables aside, and keep warm. Combine cornstarch and 1/4 cup water, stirring until smooth. Add cornstarch mixture and green onions to pan juices; cook over medium heat, stirring constantly, until thickened and bubbly. Serve roast with warm sauce. NOTE: Chinese five-spice powder is a ground mixture of five spices--cinnamon, cloves, fennel seed, star anise, and Szechuan peppercorns.