Wrap the beets together tightly in foil in 2 batches and roast them in the middle of a pre-heated 350 degree oven for 1 1/2 hours, or until they are tender. (The beets may be roasted 2 days in advance and kept covered and chilled.)
Unwrap the beets carefully and let them cool until they can be handled.
Slip the skins off the beets. Cut off the stems, and cut the beets into 1/4-inch pieces. Chill.