In this rich, sweet salad, we've included not just onions but their relatives in the Allium family — shallots, leeks, garlic, and chives. For meltingly tender results, be sure to peel off the papery outer layer, the leathery second layer, and any paper-thin membranes from the onions, shallots, and leeks.
Cooks' notes:
• Onions, shallots, and leeks can be roasted 1 day ahead and cooled completely, then chilled, covered. Reheat in a preheated 350°F oven 5 to 10 minutes.