Preheat the oven to 375 degrees F.
Wash and trim the beets, saving the greens for a salad or sauté, if desired. I leave the rootlets and a small bit of the stem end and do not dry the beets after washing.
Wrap the beets in aluminum foil, keeping a little moisture from washing the beets and drizzling with a couple of teaspoons of olive oil before sealing. If beets are not consistent in size, group and place in individual foil packets with other similar size beets. I wrap three to four medium size beets together, more if the beets are small, and two if the beets are large. This way, the beets will cook in about the same time, but if there is a vast difference in size, the beets can easily be removed from the oven as they are done.
Place the packet(s) on a baking sheet, and roast in the oven until cooked through, approximately 45 to 60 minutes, depending on size. The tip of a knife or a skewer should easily pierce the beet, yet you should feel a hint of firmness towards the center.
Remove from the oven, let cool for 10 minutes, and then peel and slice, dice, or cut into wedges.