In a 3 1/2 quart slow cooker, combine the catsup, honey, vinegar, soy sauce, five-spice, onion, ginger and garlic. Position a broiler rack 6 inches from the source of heat and preheat the broiler. Broil the ribs, turning once, until browned, about 10 minutes. Tranfer the ribs to the slow cooker. Stir to coat the ribs with the sauce. Cover and slow cook until the ribs are tender, 5-6 hours on low. Transfer the ribs to a platter and cover with foil to keep warm. Skim the fat from the surface of the sauce. In a medium saucepan, bring the sauce to a simmer over medium heat. Cook until reduced to about 1 cup, 6 to 8 minutes. Stir in cornstarch mixture, and cook just until thickened. Pour the sauce over the ribs and serve immediately with hot cooked rice.