I thought my three-onion chicken salad was a triumph. Red onions for their bite, scallions for their grassy brightness, pickled onions for a puckery jolt of acid. It had crunch, it had sharpness, it ...

To some, an onion is simply an onion. And it's true: in a pinch, most can be used interchangeably. But those who cook for a living know there's a bit more beneath the peel than that. "There are only ...