Pennsylvania Sweet Potatoes In Tangy Sauce

Place sweet potatoes in a large kettle and add water to cover. Cook over medium heat until barely tender; drain.
Peel and cut potatoes into fourths. Arrange in a medium size casserole.
Preheat oven to 350F.
While potatoes are cooking, combine sugars, ginger and cornstarch in a small saucepan. Add pineapple juice and lemon juice.
Stir over medium heat until sugars are dissolved and mixture starts to bubble; stir in margarine.
Pour sauce over potatoes.
Bake uncovered 50 to 60 min or until sauce is thickened.