Cook bacon until crisp, remove from skillet. Add onion to 1 tbs. Bacon drippings, cook until tender. Blend in cornstarch, salt and mustard. Drain beans, reserving 1/2 c. Liquid. Stir in reserved bean liquid. Cook, stirring constantly until thickened and translucent. Blend in sugar and vinegar. Add beans. Heat through. Top with crumbled bacon and chopped egg.