Onion Gratin

A simple and delicious way to use onions as a vegetable, one that long ago became part of the Middle American repertoire but has sadly dropped out. Time for a revival?

This dish is unquestionably best with small onions—pearl onions—or with cipollini, the squat Italian variety, or the very fresh spring onions, usually sold only at that time of year and looking like scallions on steroids. It will work almost as well with leeks, which should be trimmed first, then parboiled for 2 or 3