Drain liquid from beets into a measuring cup.
Add enough water to make 2/3 cup.
In a deep 1 1/2-quart casserole, mix cornstarch, sugar and salt.
Gradually add beet liquid and vinegar; stirring smooth.
Microwave, covered, 1 1/2 minutes.
microwave 1 minute, stirring after 30 seconds.
Add beets; heat, uncovered, 3 minutes.