Slice onions into very thin slices. Combine onions and sugar in a heavy non-stick skillet. Cook, uncovered, over medium-high heat for about 25 minutes or until onions turn golden and start to caramelize, stirring frequently. ? Stir in wine and vinegar. Bring to a boil over high heat, reduce heat to low and cook for about 15 minutes or until most of the liquid has evaporated, stirring frequently. Season to taste with salt and pepper. Remove jars from canner and ladle relish into jars leaving a 1/2 headspace. Process in water bath canner for 10 minutes for half-pint jars. Makes 2 cups