French onion soup isn’t difficult to make, but it does take some time. You’re looking at 45 minutes to caramelize the onions and another 90 minutes to simmer for best flavor.
Take your time on the onions, you want them a dark walnut color. And we must talk broth/stock—taste first if you’re going to use store-bought, many taste terrible, and you don’t want to ruin all your hard work. Check the freezer at your grocer for high quality options. For shelf-stable bone broths and broths, I like Bare Bones (update 2023), Imagine over Pacific, and Swanson’s low-sodium fro chicken broth.
French Onion Soup Gratinée
adapted from Julia Child's French Onion Soup in The Way To Cook
- 4 or 5 large yellow onions (about 2½ pounds total), peeled, halved, then sliced no thinner than 1/8" cut pole-to-pole, not crosswise for best texture
- 3 tbsp unsalted butter
- 1 tbsp olive oil, avocado oil, or other cooking oil
- 1/2 tsp granulated sugar
- 2 tbsp all-purpose flour
- 10 cups beef broth or stock, at least 2 cups of which should be hot homemade or purchase high quality bone broth combined with some water, see notes
- 1 cup dry white French vermouth
For serving: Cognac (a teaspoon or two for each bowl), buttered and toasted baguette slices (or other crusty bread, like a levain), grated Swiss cheese (Gruyère is nice)
Melt the butter and oil in a large dutch oven or stockpot set over medium heat. Add the sliced onions, stir them around, cover the pan, and cook slowly until tender, about 10 minutes.
Remove the lid from the onion pot, increate heat to medium-high, sprinkle in the sugar, and cook the onions until medium brown in color and caramelized, stirring frequently, about 45 minutes.
Sprinkle the flour over the onions and stir for 3 or 4 minutes. Remove pot from heat and stir in 2 cups of hot stock. Return pot to heat and bring to boil. Add remaining stock and vermouth. Cover loosely and simmer very slowly for 90 minutes, adding a little water if the liquid reduces too much.
To gratinée serving bowls: Preheat oven to broiling; position rack about 6 inches from heat. Pour a teaspoon or two of Cognac into each serving bowl. Ladle in the soup, about two-thirds full, and set on a rimmed sheet pan. Float a slice of toasted bread in each bowl (perhaps 2 baguette slices will fit) and sprinkle with grated cheese. Broil a few minutes until cheese is bubbly and starting to brown. (Alternatively, bake in 375° oven until cheese is melted, remove from oven, and brown the cheese using a hand-held butane torch.)
Recipe Notes / Tips
- Don't add extra salt if you're using concentrated stocks or broths, as they are often very salty. If you're using homemade stock or broth, add ½ teaspoon of salt with the sugar.
- If you're buying broth, keep in mind that you can probably dilute with water instead of buying exactly 10 cups of broth. It is all going to depend on the quality and intensity of what you buy. For example, a beef demi-glaze is very concentrated and you can get by with one or two small containers and build up to the "10 cups of broth" called for in the recipe with water. There are some high quality bone broths available now, like Bare Bones, which comes in 16-ounce shelf stable bags/boxes now. They are quite expensive, because they are made with high quality ingredients and aren't cut with as much water as a "beef broth" usually sold in 32-ounce boxes. So, for this soup, I would use two 16-ounce containers of Bare Bones bone broth and make up the rest, 6 cups, with water.
- To toast the bread, slice a baguette on the diagonal about half-inch thick, lightly butter one side and set on a rimmed sheet pan. Bake 375° for 5–10 minutes until crisp. To make things even easier, put the cheese on top of the baguette slices (and bake) instead of gratinée-ing the bowl. Put the cheese toasts in the bottom of each bowl, then ladle in the hot soup.