In a small glass bowl, mix cornstarch and salt.
Stir in beet juice (or water).
Microwave on high for 1 minute or until thickened, stirring occasionally.
Add vinegar, honey, and butter.
Place beets in a 1 ½ quart casserole. Pour sauce over beets. Cover and heat on high 1-2 minutes or until heated through.
Do not uncover; let stand for 10 minutes. Reheat 1 minute on high before serving.