When I was learning to cook in my Italian-American family, dinner always began with onions (and often garlic) sweating, or cooking over low heat, in olive oil. Back then, I never thought about what was happening on a chemical level—that the sugars in the onions were turning even sweeter because of the heat; that the oil would carry the flavor of the onions throughout the rest of the dish—but as I started reading cookbooks, it became clear that cooks take pains to describe exactly how onions should be cooked: translucent, or golden, or browned. When I was working on a cookbook with the Venetian chef Mara Martin years ago, she would correct me while I was translating her recipes. "Browned is too much!" she insisted—but gold was not enough. "Abbronzate," she'd say in Italian. Bronzed. It's the difference between what the Italians call a battuto—a base of onions, with celery, carrots, and other seasonings that's briefly cooked in the beginning stages of a soup, a sauce, a risotto—and a soffritto, where the onions are taken to a deeper level of gold. All across the globe, cooks start dishes this way: There's the French mirepoix of onions, celery, and carrots; the Cajun trinity of onions, peppers, and celery; the way southeast Asian cooks start curries and other dishes by slowly cooking a spice paste made with aromatics and lots of minced shallots; or how Middle Eastern cooks sweat onions in fat and then add dry spices. When I was in Morocco I learned to start a tagine by cooking onions with saffron in a pan and then transfer them to the oven, where their flavors mingled as they stewed with other ingredients, like chicken and olives and lemons.