The sweetness is twofold here: The beets caramelize during baking, becoming wonderfully sweet, and the slight sweetness of the balsamic vinegar then underscores them.
Preheat the oven to 400°F. Trim off the leafy tops of the beets, but leave about an inch of the stem attached. Wash the beets well, scrubbing them with a vegetable brush, but leave them unpeeled.
Tear off large sheets of aluminum foil. Place 2 or 3 bee