Instructions
- Preheat the oven to 425 degrees.
- Cut the onions in half lengthwise, leaving the skins on.
- In a 12 inch oven proof skillet, heat the oil until smoking.
- Place 4 onion halves cut side down in the skillet.
- Cook without moving them, over medium heat, until dark golden brown, 7 to 8 minutes.
- Add the vinegar and place the skillet in the oven.
- Bake until the onions are soft, 15 to 20 minutes.
- Remove the onions from the pan immediately.
- Place cut side up on a cool plate.
- Pour the syrup that has formed in the pan over the onions and cool to room temperature.