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French Onion Gruyère Baguette Sandwich

by Jessie Daye

First published: January 3, 2025 | Updated: June 22, 2026

French Onion Baguette with extra Gruyère You can make ahead and bake this sandwich in the oven so it’s perfect for a party or even a Super Bowl gathering. Add roast beef if you wanted some added protein. Recipe below!

French Onion Gruyère Baguette Sandwich

Author: Jessie Daye
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Ingredients

  • (2) yellow onions (4 cups) peeled and thinly sliced
  • 2 tbs thyme
  • 2 teaspoons Kosher salt
  • 1 teaspoon black pepper
  • 2 teaspoons Cooking sherry
  • 2 cups Beef stock
  • ½ teaspoon cornstarch + 1tbs water
  • 4-6 tablespoons salted French butter
  • 8 oz shredded Gruyère cheese
  • (1) 16”-18” French baguette

Method

  1. In a large skillet over medium-high heat, melt 2 tablespoons butter. Add the onions and season with salt and pepper. Cover and cook, stirring once or twice, until the onions are softened, 3 to 5 minutes.
  2. Uncover, reduce the heat to medium-low, and cook, stirring occasionally, until golden brown, 20 to 25 minutes. If the onions look like they might burn, add a tablespoon of water, scraping up any browned bits that are stuck to the bottom of the skillet. Once the onions are done, deglaze the skillet with sherry wine and cook until the liquid has evaporated, about 1 minute.
  3. Add the beef stock and increase the heat to medium-high. Allow the mixture to come to a boil, then reduce the heat to a simmer and cook for another 5 minutes.
  4. Mix the cornstarch in a small bowl with a teaspoon of water to form a slurry, then add it to the onion mixture. Cook for another two minutes, allowing everything to thicken.
  5. Using a slotted spoon, scoop the onions out of the broth, and place them in a large serving bowl and set aside. Add the au jus to a small bowl for dipping.
  6. Preheat your oven to 450 F.
  7. Slice your baguette horizontally and slather with salted butter. Layer in your sautéed onions and top with shredded Gruyère cheese and thyme if desired. Press the sandwich together and roll in foil or parchment paper and set on a baking sheet. Bake for 6-10 minutes until cheese is melted and sandwich is hot.
  8. Slice and serve immediately with au jus.

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Hi, I'm Jessie. 

I’m a Los Angeles mama, home renovator, and lifelong creative, sharing the things that make everyday life a little more beautiful. I believe food is one of the best ways to bring people together, which is why I love cooking: it turns an ordinary Tuesday into something worth remembering. From recipes I make on repeat to DIY projects, home design, and a little bit of real life in between — welcome to my corner of the internet. I’m so glad you’re here.

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