French onion soup is one of the most warm and decadent wintery dishes imaginable. Rich caramelized onions are suspended in a savory thyme-scented broth and topped with a crusty crouton draped in melted cheese. A quintessential cold-weather comfort food, this bistro classic can be a great addition to any meal plan, unlike many other traditional stick-to your-ribs offerings.
Onion soups have been common fare for centuries. Indeed even before the advent of modern traditional science, folks figured out that onions are a powerful and restorative medicinal food, rich in what we now know to be antioxidants, prebiotic plant fiber and powerful antiviral and antibacterial compounds. As for the famed soupe a l'oignon there are stories that Louis XV himself came up with the dish when his famished hunting party stopped at his lodge to find the cupboards bare except for some onions, butter and Champagne (though I have a hard time envisioning King Louis with his sleeves rolled up chopping onions).
It seems more likely that the version we think of today as French onion soup likely originated in Les Halles, the sprawling outdoor Parisian market founded in 1135 that served as Paris's central market hub until it was demolished in 1971. Parisians from all walks of life converged at the market – aristocrats in evening dress on their way home from a night of frivolity, bloody butchers and working people heading to or from work in the pre-dawn hours. Amongst the produce hawkers and merchants were soup stalls selling thin soup made from scraps of cabbage, carrots and often burnt bits of onion, ladled into a cup over a hunk of dry bread. At some point the bistros surrounding the Les Halles market began serving an upgraded version of the humble onion broth, adding a gratinée of bubbly brown cheese, thus creating what we now think of as soupe a l'oignon, or French onion soup. It gained a reputation as a hangover cure and has since become a traditional feature of many French weddings, served at the end of the reception in the predawn hours to sober up the guests before they headed home.
Centuries later this iconic soup can be found in restaurants around the world. There is an English iteration of this soup as well, equally delicious and with roots that are likely just as ancient. That version uses a mixture of lightly caramelized yellow onions, shallots and leeks, deglazed with a brown ale and simmered in a savory broth before being topped with a gratin of whole-grain bread and sharp aged cheddar.
Although one may not equate this hearty soup with diet fare, it can actually be a healthful addition to almost any meal plan. Before the addition of cheese and bread, a large bowl of onion soup only contains about 85 calories. Add a thin slice of baguette and a sprinkling of cheese, and the count is still just under 300 calories. Prepared onion soup freezes perfectly and is wonderful to have on hand to help whip up simple cooked meals. Add thawed onion soup to a roast in a slow cooker or multi-cooker and you're ready to press start. Or use it as the cooking liquid in a pot of barley risotto with a few handfuls of baby spinach tossed in at the end of cooking for a nourishing weeknight supper that requires minimal prep.
Soupe a l'oignon (French onion soup)
1 tablespoon butter or olive oil
3 pounds yellow onions, not sweet, sliced
½ teaspoon salt
1 teaspoon sugar
1 bay leaf
1 teaspoon dried thyme
½ cup dry wine, white or red
8 cups low-sodium broth or water
2 tablespoons cognac (optional)
12 ounces grated parmesan or gruyere (a mixture is good)
6-8 slices crusty French bread, stale or lightly toasted
Melt the butter in a heavy-bottomed soup pot or Dutch oven over medium-high heat. Let the butter brown slightly, then immediately add the onions, salt, sugar, bay leaf and thyme. Increase heat to high and sauté for a minute to give the onions a good sear, then add the wine to deglaze the pan, stirring up any brown bits that may have stuck to the bottom. Reduce heat to low and continue to cook for about 45 minutes, stirring every 5-10 minutes and adding a splash of water or wine as needed to deglaze.
Once the onions have reached a deep mahogany color, add the broth or water and cognac and increase the heat. Bring the soup up to boil, then reduce to a simmer and cook for 30 minutes. Season to taste with salt and pepper. At this point the soup can be refrigerated for up to a week or frozen for several months.
When ready to serve, preheat the broiler and bring the soup up to temperature. Ladle the soup into oven-safe bowls and place them on a baking sheet. Float a slice of bread on top of each bowl of soup, then sprinkle generously with cheese. Place the bowls under the broiler until the cheese is golden brown and bubbly (watch them closely). Remove from the oven and sprinkle with chopped parsley, if desired, before serving.