1. Drain beets, reserving liquid. Add enough water to beet juice to make 2/3 cup liquid.
2. Combine cornstarch salt, and pepper in saucepan. Add liquid and vinegar. Stir until smooth.
3. Cook, stirring constantly, until mixture thickens and boils. Boil 1 minute, stirring.
4. Add sliced beets and sugar; heat through.