Prep 10 mins
Cook 1 hr 33 mins
- Preheat the oven to 375 degrees.
- Remove the outermost layer of onion skin, spray the onions with cooking spray, and sprinkle them with salt and pepper.
- Place the onions close together in a baking dish and roast, uncovered, about 1 1/2 hours, until tender when pricked with a fork.
- (The onions will release their juices while roasting and should be soft but not mushy.) Remove the onions from the pan and set aside.
- Add the water to the baking dish and stir to loosen and collect the pan juices; transfer to a small saucepan.
- Add the vinegar and cook over medium heat for 2 to 3 minutes, reducing the mixture to about 1/4 cup syrup.
- Cut the onions in half lengthwise and brush the cut surface generously with the syrup, allowing it to sink down into the layers.
- Sprinkle with salt and pepper to taste and serve.