Sweet onions like Vidalia (from Georgia) and Walla Walla (from Washington) were once a somewhat esoteric ingredient. These crisp, sweet (well, relative to other onions anyway) vegetables were available locally in the regions where they grew, but they didn't travel much. Part of this was because of their perishability (sweet onions do not keep as well as other onions) and part of it was because there was no consumer demand.

Well, that's certainly all in the past, because most supermarkets now routinely carry sweet onions. Starting in the spring, there is a big influx of sweet onions from places in North America, but in the winter, sweet onions come from South America.

If you really know your onions, you are already familiar with the OsoSweet onion, which grows in the Andes in Chile. But if you haven't ever had an OsoSweet, then hurry up, because the season for this winter onion lasts only through the end of March.