Have ready a large bowl of ice water. Bring a 4- to 5-quart pot of water to a rolling boil and add the onions. Cook for 1 minute, drain, and transfer to the bowl of ice water. Swish the onions around until they’re chilled. Remove them from the water and peel; the skins should come off easily when you rub them with your fingers, though some may need a paring knife.
Put the onions in an 8-inch-wide, 3- to 4-quart saucepan and arrange snugly. Add the butter, honey, cayenne, 1/2 tsp. salt, and enough water to just cover the onions (about 2 cups). Bring to a boil over high heat.
Cook over high heat, shaking the pan occasionally, until the liquid has reduced to a syrupy glaze and the onions are tender, about 10 minutes. (If the glaze is done before the onions, add about 1/2 cup water and continue to cook. If the onions are done first, remove them and continue to boil the liquid until syrupy.)
Lower the heat to medium low, add the white wine vinegar and toss to combine. Season to taste with salt and serve. (The glazed onions can be kept warm, covered, for about 20 minutes.)