Classic French Onion Soup with Gruyere Gratin

I had my very own Julie and Julia moment this week via her often imitated French Onion Soup recipe. I love instant gratification as much as the next girl, but this soup was worth every single stir, every tear and sniffle, and most certainly worth dragging the big soup pot out from the back of the cupboard. It’s rare that I will follow a recipe to the letter, but there are a few exceptions. Julia Child definitely gets first chair in my symphony of culinary heroes, and the respect of a mostly unadulterated recipe preparation.

For all of it’s simplicity, onion soup is transcendentally delicious. I’m loosely quoting Deb over at Smitten Kitchen (whose recipes I will also follow) when I say that onion soup is a gourmet dish that anyone can prepare. You need not fancy knife skills, or culinary je ne sais quoi to speak of. Onion soup requires only low heat and patience, yet repays with the kind of outcome you thought only came from gourmet restaurant kitchens.

The key to success with this delicious onion soup is, as I said before, patience. The onions require a very long caramelization, in which they develop a rich flavor which will entirely carry the flavor profile of the dish. I implore you not to skimp here. This is really where all of the work is, and the effort is not great.

Recipe is directly from Smitten Kitchen, and is a slightly adapted version of the original Julia Child recipe. I usually hesitate to post recipes that I have not altered in any way, but this soup really needed no changing. I added the fresh thyme, but that’s it.

Onion Soup (Soupe à l’Oignon)
Adapted from Mastering the Art of French Cooking

Recipe serves 6


  • 1 1/2 pounds (about 5 cups) thinly sliced yellow onions
  • 3 tablespoons unsalted butter
  • 1 tablespoon (15 ml) olive oil
  • 1/2 tablespoon fresh chopped thyme
  • 1 teaspoon salt, plus additional to taste
  • 1/4 teaspoon granulated sugar (helps the onions to brown)
  • 3 tablespoons all-purpose flour
  • 2 quarts (8 cups or 2 liters) beef stock
  • 1/2 cup dry white vermouth (or dry white wine)
  • Freshly ground black pepper
  • 3 tablespoons (1 shot) cognac or brandy (optional)

To finish:

  • 1 tablespoon grated raw onion
  • 6 ounces grated gruyere cheese
  • 12 to 16 1-inch thick rounds French bread, toasted until hard


  • Melt the butter and oil together in the bottom of a 4- to 5-quart saucepan or Dutch oven over moderately low heat.
  • Add the onions, toss to coat them in oil and cover. Reduce the heat to very low and let them slowly steep for 15 minutes. They don’t need your attention through this process.
  • After 15 minutes, uncover the pot, raise the heat slightly and stir in the salt and sugar. Cook onions, stirring frequently, for 30 to 40 minutes until they have turned an even, deep golden brown.
    • Remember: no skimping on this step!
  • Sprinkle caramelized onions with flour and cook, stirring, for 3 minutes.
  • Add the vermouth
  • Add stock bit by bit, stirring between additions to avoid flour lumps.
  • Season to taste with salt and pepper, and add thyme
  • Bring to a simmer and simmer partially covered for 30 to 40 more minutes, skimming if needed.
  • Correct seasonings if needed
    • Go easy on the salt here. The cheese will add salt, and the flavor will intensify as it cools a bit.
  • Stir in the cognac
    • I definitely recommend the cognac addition! 
This soup is flavor rich enough to be enjoyed as is. However, if you’re feeling fancy here’s how to gratinée, aka “the French restaurant experience”

For the Gratin:
  • Preheat oven to 325 F
  • Arrange six ovenproof soup bowls or crocks on a large, foil-lined baking sheet.
  • Bring the soup back to a boil and divide among six bowls.
  • To each bowl, add 1/2 teaspoon grated raw onion and a tablespoon of grated cheese. Stir to combine.
  • Float croutons on top of your soup bowl attempting to cover the surface.
  • Mound grated cheese on top of it; about 1 ounce per bowl.
    • Julia Child recommended 1/2 cup should be divided between 6 bowls, but I prefer more. My favorite restaurant version always comes with a generous helping of bubbling cheese on top, and at 90 calories for an entire ounce of good gruyere, it’s easy to justify.
  • Bake soups on tray for 20 minutes until cheese is melted and bubbly.
  • Finish under the broiler for a couple of minutes for extra color if desired.

French onion is my all time favorite soup. It has been since I was a child. If I see it on a menu, I will order it. Hands down favorite. That may change now though, because this simple homemade version has made me realize how many times I have been served a truly sad bowl of soup. I will certainly be making this at home more often after this experience.

Yummy bubbly, browned cheese.

If you have leftovers (I did!) try freezing in cubes, and mixing in to your next meatloaf for a caramelized onion flavor boost!

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23 thoughts on “Classic French Onion Soup with Gruyere Gratin

  1. this is by far one of my favourite foods. Having had some recently in France and at a friends house here in Italy, it also changes from place to place depending on the ingredients. I love the way you start with a recipe and then take it where you want it.

      • And if you go in the summer find a place higher up…some there say it’s a winter only food, ignore them. That’s why the invented air conditioning

    • Thank you! I love them too. I stalked the clearance section of my local cooking store (sur la table) until they showed up =) I love French onion soup! If you like caramelized onions, I reckon you’d like it too.

  2. I love french onion soup!(Wait.. What do not I like…. 😉 ) anyway it looks so wonderful! If I do not have thick enough pot as you have… what can I do? um…any suggestion? Thanks!

    • You can really make this in any soup pot, the onions might just take a bit longer to caramelize. I like the thicker ones for their even heating, but it’s not a necessity – just watch out for hot spots. You could also caramelize the onions in a skillet with a thick bottom and transfer to your soup pot when you’re ready to simmer.

      Hope this helps!


    • Thank you! What a sweet thing to say. I think gruyere may be my favorite as well. It’s so versatile! It melts/browns beautifully. I made a bechamel with gruyere once, and it was so good I nearly died =)

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