Place beets in a 3-quart
saucepan with water covering them by 1/2-1 inch. Cover and bring to a boil; turn
heat down slightly and let the beets simmer until cooked but not mushy - about
20-25 minutes. Remove the beets, saving the cooking liquid. Remove outer peel
from beets under running water with a paring knife; it's much easier to do this
after they have cooked rather than before! Slice the beets in 1/4-inch slices.
In a saucepan or deep non-stick
frying pan, stir together the cornstarch, sugar, salt and pepper. Add the
vinegar and reserved cooking liquid from the beets, stir to completely
incorporate the dry ingredients (I use a gravy whisk). Cook and stir constantly
until the mixture is boiling and beginning to thicken. Boil gently and stir for
one minute, then add the beets along with the butter; heat through before serving.
(Since beets will stain
anything they come in contact with, be careful!)