In skillet, cook bacon. Remove and drain. Pour off all but 3 T bacon fat, add onion and celery and stir fry 1-2 minutes. Blend in flour. Add juice and vinegar, stirring until mixture thickens. Add sugar.
Preheat oven to 350 deg F. Place potatoes, apples, and crumbled bacon in greases 1 1/2 qt casserole. Add skillet mixture, mixing lightly.
