Cipollini are small, sweet onions. If you don’t have any, use small onions, unpeeled, instead.
Preheat oven to 325°F. Place unpeeled onions, bay leaf and ½ the olive oil in a bowl. Salt and pepper. Mix well.
Spread vegetables evenly and attractively on a roasting dish and sprinkle with remaining olive oil.
Place the roasting dish in the center rack of the oven. Roast until almost cooked, between 1-1¼ hours. Pour balsamic vinegar onto the onions and cook 10 minutes more.
Garnish with parsley leaves and a splash of olive oil.
A variation of the Squash, Fennel and Celery Root Tian from The Spice Trekkers Cook at Home