How to make French onion soup
By Becky Krystal 
Oct 4, 2019
Few soups get people as misty-eyed as French onion.
Sure, I count myself among the many who cry while slicing pounds and pounds of onions. Despite the waterworks, it's hard to resist the result: a rich, fragrant, deeply coloured pot of comfort. The best renditions are so beautiful, they might bring a tear to your eye - at least metaphorically.
This Fast French Onion Soup from kitchen wizard and Serious Eats chief culinary adviser J Kenji López-Alt is speedier than a traditional preparation, and it doesn't sacrifice flavour in the interest of time.
His method, which I took from his impressive 2015 cookbook, "The Food Lab", uses sugar, baking powder and increased heat to speed up the onion caramelization process.
The sugar (only 1 tablespoon, don't worry!) contributes sweeter, deeper, faster-developing flavour. Baking powder speeds up browning (that Maillard reaction you may have heard about) and leads to softer onions by breaking down the cells faster.
And heat?
Well, naturally, food cooks faster at a higher temperature, and the addition of water here reduces the risk of burning and better distributes all the sugars. As the subtitle of the book says, "better home cooking through science."
FAST FRENCH ONION SOUP (Serves 4-8)
1 tablespoon sugar
2.25kg yellow onions, thinly sliced
2 tablespoons unsalted butter
1/4 teaspoon baking powder
2 teaspoons kosher salt, plus more as needed
1/2 cup water
1/4 cup dry sherry
6 cups chicken broth
2 bay leaves
6 to 8 sprigs fresh thyme
Freshly ground black pepper
1 baguette, sliced 1-inch thick and toasted
230g Gruyère or Swiss cheese, grated
Method
Pour the sugar into a large Dutch oven and cook over medium-high heat, swirling the pot gently as the sugar melts, until it is completely liquid and a golden-brown caramel.
Add the onions and cook, stirring with a wooden spoon and tossing constantly until they are evenly coated in the caramel, about 30 seconds.
Add the butter, baking powder and 2 teaspoons salt and cook, stirring occasionally, until the onions are a light golden brown and a brown coating has started to build up on the bottom of the pot, about 10 minutes.
Add 2 tablespoons water and scrape the browned coating from the bottom of the pot. Shake the pot to distribute the onions evenly over the bottom and cook, shaking occasionally, until the liquid evaporates and the browned coating starts to build up again, about 5 minutes.
Add 2 more tablespoons water and repeat, allowing the coating to build up and scraping it off, then repeat two more times. (Reduce the heat as needed if the coating is burning and turning black.) By this point, the onions should be deep brown. If not, continue deglazing and stirring until the deep brown colour is reached.
Add the sherry, chicken broth, bay leaves and thyme, bring to a boil, and reduce the heat to low, so the soup is at a gentle simmer. Simmer, uncovered, until the liquid is deeply flavoured and slightly reduced, about 15 minutes. Season to taste with salt and pepper. Discard the bay leaves and thyme.
To serve, heat the grill. Ladle the soup into four grill-proof bowls. Float 1 or 2 bread slices on top of each bowl and cover with the grated cheese. Grill until the cheese is melted, bubbly and golden brown in spots.
Serve immediately.
The Washington Post