When I first began making this delicious condiment, I used big red torpedo onions. Today I am just as likely to use locally grown Walla Walla onions or whatever other big sweet onions are available at a farmers market. The most important thing is to use onions with a high sugar content. If, after lengthy cooking, your onions takes a bit flat, without any sweetness, consider sprinkling a tablespoon or two of granulated sugar over the onions a few minutes before adding the liquids.