In a large straight-sided saute pan over medium-high heat, melt butter and add onions. Season, to taste, with salt and pepper. Saute until nicely browned then add the wine and vinegar. Bring to a boil, cover, reduce heat and simmer until onions are completely cooked through and tender, about 15 minutes. Remove lid, turn heat up and let the liquid reduce and thicken until it forms a glaze and coats the onions well.
Recipe courtesy of Sunny Anderson, 2008