Preheat oven to 425°. Cook onions in boiling water to cover 3 minutes; drain. Rinse thoroughly under cold running water. Let stand 5 minutes.
Cut off root end of 1 onion. Using a towel, gently squeeze pointed end of onion toward root end, slipping outer peel off of onion. Discard outer peel. Repeat procedure with remaining onions.
Melt butter in a 12-inch ovenproof skillet in a 425° oven 5 minutes. Stir in onions.
Bake onions at 425° for 15 minutes. Stir together wine and next 4 ingredients. Stir wine mixture into onions, and bake 35 to 40 minutes or until caramelized. Stir onions to coat and loosen particles from bottom of skillet.