Onion bulbs in general are basically the underground base of the plant stem. As daylight hours lengthen (past 6), the plant stops making leaves and starts devoting resources to the bulb which swells. These red violet vegetables in particular are the mildest and sweetest of the onion family. This versatility means they’re often used in both raw and cooked dishes. However remember that cooking an onion diminishes its flavor while to a lesser extent seasoning neighboring ingredients. This is why many cooked recipes will favor a yellow or white onion instead.