Home Recipes French Onion Grilled Cheese Sandwich

French Onion Grilled Cheese Sandwich

With buttery caramelized onions, gooey melted cheese, and golden toasted bread, this decadent French onion grilled cheese sandwich is 100% drool-worthy.

Imagine thick slices of crusty sourdough enveloping a heavenly filling of deeply caramelized onions, their sweetness perfectly balanced by a hint of beef broth. 

And then, the pièce de résistance – a luscious blend of nutty Gruyère and sharp cheddar, melted to gooey perfection.

Are you drooling yet? I know I am!

Sliced French Onion Grilled Cheese Sandwich overflowing with cheese and caramelized on a white plate
Enter your email below & we'll send it straight to your inbox.

Why You’ll Love This French Onion Grilled Cheese Sandwich

Rich Flavor and Cheesy Goodness: From the deeply flavorful caramelized onions to the combination of Gruyère and sharp cheddar, this sandwich packs an incredible punch of savory, sweet, and umami flavors.

Gourmet Experience: This French onion grilled cheese sandwich offers a sophisticated twist on a classic comfort food. And while it’s messy, it definitely looks gourmet. 

Versatile Crowd-Pleaser: It’s an upscale yet approachable dish that can be enjoyed for lunch, dinner, or even as an appetizer, appealing to a wide range of palates.

Thinly sliced caramelized onions with butter in a white bowl, sour bread on the side.


  • Hearty Sourdough Bread: This sturdy foundation is rustic, tangy, and ready to embrace all that cheesy goodness.
  • Medium Yellow Onions: Sliced thin and caramelized slowly for sweet, jammy flavor.
  • Butter: Brings the richness. Feel free to use salted butter, but then omit the extra salt in the recipe.
  • Olive Oil: A splash of liquid gold adds depth to the onions and keeps the butter from burning.
  • Sugar: The secret weapon – just a pinch enhances the onions’ natural sweetness.
  • Salt and Black Pepper: The dynamic duo that seasons the onions to savory perfection.
  • Fresh Thyme Leaves: A pop of herbal freshness. 
  • Beef Broth (Dry Sherry or Water): Beef broth is key to the soup’s signature flavor, so it’s vital if you ask me. But feel free to swap in sherry or water if that’s all you have.
  • Gruyère and Sharp White Cheddar Cheese: The ultimate dream team. Nutty, sharp, and oh-so-melty, Gruyère brings the classic French onion flavor, while sharp cheddar adds a tangy kick.
Close up of a French Onion Grilled Cheese Sandwich on a chopping board

How to Make French Onion Grilled Cheese Sandwich

This mouthwatering creation takes the beloved flavors of French onion soup and transforms them into a handheld, melty masterpiece.

But since it’s chock-full of caramelized onions, it does take a bit of time to make. Luckily, most of it is hands-off!

1. CARAMELIZE: Melt the butter with the oil and mix in the sliced onions. Cook and stir in 5-minute intervals until soft, golden brown, and jammy. Add the seasonings and beef broth, remove from the pan, and wipe it clean.

2. TOAST: Melt the rest of the butter and oil in the same skillet. Add the bread slices and toast until lightly golden. 

3. MELT: Flip the bread and sprinkle the cheeses evenly over the top. Cover the pan and cook until melty. 

4. ASSEMBLE: Take the bread out of the skillet and spread the caramelized onions over 2 slices. Top with remaining slices, and press gently.

5. SERVE: Cool for 1-2 minutes, then slice and dive in!

Sliced in half French onion grilled sandwich with melted cheese.

Tips For the Best French Onion Grilled Cheese

Whether you’re a die-hard grilled cheese enthusiast or simply a lover of all things deliciously comforting, this French onion grilled cheese is sure to become a new favorite. 

But before you get stirring, I have a few tips and tricks to check out.

  • Choose sturdy bread: Sourdough is the best choice as it’ll hold up well to the heat and maintain a good texture even with the soft, gooey fillings. But you can also try a ciabatta or a crusty baguette. Texas toast might work, too!
  • Use quality cheese: Gruyère and sharp white cheddar are excellent choices. Other good options include Gouda, Fontina, Havarti, or Monterey Jack. Shred them from a block for the best cheese pull!
  • Caramelize the onions slowly: It’s a pain, but low and slow wins the race. Trust me, if you try to speed things up, the onions will simply burn. So allow for about 20-30 minutes. 
  • Deglaze the pan: A little beef broth lifts the brown, flavorful bits off the pan and enhances the savory notes in the dish. 
  • Add mayo: Spread mayo on the bread for a crispy, golden crust.
  • Cook over medium-low heat: This ensures even cooking and melting of the cheese without burning the bread.
  • Let rest before slicing: Allow the sandwich to rest for a minute or two before cutting to prevent the cheese from oozing out.
  • Optional mix-ins: Add ingredients like cooked apples, mushrooms, or bacon for extra flavor and texture.
  • Serve with: Pair the sandwich with a green salad, tomato soup, or salty potato chips for a complete meal.

More Grilled Sandwiches You’ll Swoon Over

Buffalo Chicken Grilled Cheese Sandwich
Sloppy Joe Grilled Cheese
Pizza Grilled Cheese
Air Fryer Grilled Cheese
Bacon Grilled Cheese Sandwich

French Onion Grilled Cheese Sandwich

Course: Main CourseCuisine: American, French


Prep time


Cooking time




Enter your email below & we'll send it straight to your inbox.

With buttery caramelized onions, gooey melted cheese, and golden toasted bread, this decadent French onion grilled cheese sandwich is 100% drool-worthy.


  • 4 tablespoons unsalted butter, divided

  • 4 tablespoons olive oil, divided

  • 3 medium yellow onions, peeled, halved and thinly sliced

  • 1 teaspoon sugar

  • 1/2 teaspoon salt

  • 1/4 teaspoon black pepper

  • 1 teaspoon fresh thyme leaves, chopped

  • 1/4 cup beef broth, dry sherry, or water

  • 4 slices hearty sourdough bread

  • 6 oz Gruyère cheese, shredded

  • 4 oz sharp white cheddar cheese, shredded


  • Make the onions. Melt 2 tablespoons of butter with 2 tablespoons of olive oil in a large heavy skillet over medium heat. Add the sliced onions, stir to coat them in the fat, cover the pot, and cook for 5 minutes until the onions soften.
  • Remove the lid and add the sugar, salt, and pepper. Stir well and put the lid back on. Reduce the heat to medium-low and cook in 5-minute intervals, lifting the lid to stir each time, until they reach a deep golden brown color, about 20 minutes.
  • Add the broth to deglaze the pan, scraping up any brown spots from the bottom with a wooden spoon. Cook for about 1 minute, then stir in the thyme and remove the skillet from the heat. Transfer the caramelized onions to a heatproof bowl and carefully wipe out the skillet with a paper towel.
  • Make the grilled cheese. Warm the remaining oil and butter in the skillet over medium-low heat.
  • Place the 4 slices of bread in the skillet and cook until lightly toasted, about 2 minutes. Flip the bread, then evenly sprinkle the cheeses over each slice. Cover the skillet and cook until the bread is golden and the cheese has melted, about 2-3 minutes.
  • Remove the skillet from the heat and carefully transfer the bread to a chopping board. Spread the caramelized onions over 2 slices of bread, then gently press the tops in place.
  • Let cool for 1-2 minutes before slicing in half. Serve immediately while hot and gooey. Enjoy!


  • Low and slow is key for caramelizing the onions to bring out their natural sweetness. Don’t rush this step or they’ll burn!
  • Cooking the sandwiches over medium-low heat lets the cheese fully melt before the bread gets too dark. You can also finish them open-faced under the broiler or in a sandwich press if you have one.

Did you like the recipe?

Click on a star to rate it!

Average rating 5 / 5. Vote count: 1

No votes so far! Be the first to rate this post.


Share on social media:

We are sorry that this post was not useful for you!

Let us improve this post!

Tell us how we can improve this post?

author avatar
Kim - InsanelyGood
Hey there! I'm Kim. I love running, cooking, and curling up with a good book! I share recipes for people who LOVE good food, but want to keep things simple :)

Leave a Comment