Arrange ribs, meaty side down, in a foil lined pan. Cover and bake
for 45 minutes.
In a saucepan, combine sugar and cornstarch. Stir in vinegar, chili
sauce, water, undrained pineapple, onion, soy sauce, and mustard.
Cook and stir over medium heat until thick and bubbly; cook and
stir 2 minutes more. Remove the pan from the oven and drain the
fat from the ribs. Turn the ribs meaty side up. Spoon 2 cups sauce
over the ribs. Reserve the remaining sauce in the pan.
Cover the ribs and bake 45 minutes longer or until tender.
Remove the ribs to a platter.
Heat the sauce in the pan and serve with the ribs.