Whether it's the start of a big meal or a simple supper on its own, a bowl of French onion soup always gives me a little thrill when it arrives at the table. Served in its own special stoneware crock, gratinéed with Gruyère cheese until bubbly and golden, the soup is all the more tantalizing because it's served straight out of the oven, far too hot to eat. I have to sit there patiently (or not), inhaling the heady aroma of sweet onions and savory broth, until I can finally dip into the gooey blanket of cheese and broth-soaked bread for a tiny sip of soup.
For the longest time, French onion soup was a restaurant ritual for me, nothing I would ever bother making at home. But then I inherited my mother's set of onion soup crocks, and I was moved to put them into action. As I began reading recipes, I quickly realized that this classic bistro dish is at its heart a simple peasant soup, and that there are as many versions as there are cooks with a bag of onions and a soup pot.
The recipe that I've developed over the years isn't a carbon copy of one you might get from a French bistro—for one thing, I usually use chicken broth in place of the traditional beef broth, turning a lengthy cooking project into something I can make in about an hour and a half. I also forgo the extra flavorings that many chefs use (Cognac, sherry, or sugar, for example) because I feel that these are too much for this lighter style soup, and sometimes less is more.
My version of onion soup requires no unusual ingredients, and it fills me and anyone I serve it to with a warmth and satisfaction that few soups can match.
Caramelize onions lightly to coax out sweetness yet keep some toothiness
Choose standard yellow onions—their strong flavor becomes sweet, but not overly sweet, when slow-cooked in butter. Look for the largest onions you can find (often labeled Spanish onions) because large onions mean less peeling. I like to slice the onions by hand because I can better control how thinly they're sliced—they should be about 1/8-inch thick. But I can't deny that a food processor with a slicing blade does the job faster, if a little more crudely; just be sure to pick out any stray ends and chunks that the blade missed. A mandoline works, too.
Go light on the caramelization to preserve texture. Or for more flavor, but less toothiness, cook the onions longer.
The main trick to cooking the onions is to start out by stewing them
slowly in butter; you want to coax out their sweetness without browning
them too quickly. Expect this to take 35 to 45 minutes over medium heat,
and stay nearby so that you can stir the onions occasionally and lower
the heat if they start to brown too quickly.
How much you caramelize your onions depends entirely on personal preference. I like to take them to a deep straw color. This leaves them with some texture and toothiness, which they'll lose if you cook them down until they're almost jammy. If you prefer a more pronounced caramelized flavor, as some cooks do, simply cook the onions longer or crank up the heat slightly at the end.
Once the onions are done to my liking, I stir in a couple of teaspoons of flour. This small amount doesn't cloud the broth or thicken the soup, but it does add a pleasing touch of velvety viscosity and roundness of flavor—something I miss when making the soup with chicken broth in place of beef broth.