French Onion Grilled Cheese
This recipe for French onion grilled cheese sandwiches layers rich caramelized onions with gobs of melted cheese on buttery griddled toast. It's gooey, crisp and totally irresistible!
A grilled cheese is one of my all time favorite comfort foods, and this version is a really fun play on the classic!
The caramelized onions are the star of the show. Sweet onions get cooked down until they're jammy and deeply caramelized along with a bit of fresh thyme and a splash of Worcestershire to give them that unmistakable French onion soup flavor. A few drops of vinegar adds complexity and wakes everything up.
The jammy onions get smeared onto thick slices of bread, then layered with lots of good quality Swiss cheese or Gruyere. I usually go with 3 slices, but you can never go wrong with a little more!
Griddle on both sides until golden and the cheese is melted, and always use salted butter to add more flavor. The key to success is go low and slow! Keep the heat low to prevent the bread from burning before the cheese melts.
Try splashing a little bit of water onto the griddle and then place a bowl over top to encase the steam. This is an old diner trick that will help get your cheese to ooey-gooey perfection!
This is truly the best grilled cheese sandwich you'll ever make! You'll have some leftover caramelized onions, but they're easy to use up. Add them to your scrambled eggs and thank me later. Or, just make another grilled cheese!
For more French-inspired recipes, try this classic Flounder Meunière, a summery French Tomato and Goat Cheese Tart or my rich Beurre Blanc sauce.
Why This Recipe Works
- Jammy, slow-cooked onions add sweetness and depth that play so well with the rich cheese.
- Made with just a handful of good ingredients, so every element counts.
- A simple technique ensures the bread gets crisp and golden while the cheese melts all the way through.
Ingredient Notes
Onions - I love using a sweet onion like Vidalia since they caramelize really well, but yellow onions or Spanish onions are great too.
Cheese - This works with a lot of different cheeses. A good quality Swiss or Gruyere cheese gives that classic nutty flavor, but aged cheddar, fontina and brie all work well too.
Butter - Salted butter gives the most flavor, but unsalted butter still works.
Bread - Choose rustic, sturdy slices that can handle the cheese and onions, like sourdough or a country loaf.
Seasonings - Thyme, Worcestershire sauce and a splash of Sherry vinegar balance the sweetness of the onions. You can use a pinch of dried thyme in place of fresh if you need to, and red wine vinegar or apple cider vinegar can be used instead of sherry.
*Find the full ingredient list in the recipe card below!
Helpful Equipment
- Large skillet
- Saute pan or griddle
- Serrated knife
- Spatula
- Mixing bowl
- Measuring spoons
- Cutting board
Step by Step Instructions
- Melt 2 tablespoons of butter in a large sauté pan over medium heat, then add the onions. Stir, then cover and cook until softened, about 5 minutes. Add a splash of water and scrape up any browned bits on the bottom, then cover and cook down some more. Repeat this process several more times until the onions have started to turn deep brown and caramelized.
- Add fresh thyme, Worcestershire sauce, sugar and vinegar, then season with salt and pepper to taste. Continue cooking for 2-3 more minutes, then transfer onions to a bowl.
- Spread a layer of onions on each slice of bread. Top two pieces of bread with a folded slice of Swiss cheese. Top with more onions, then another slice of cheese, then more onions, and one more slice of cheese. Place the remaining slices of bread on top and gently press down.
- Preheat a large sauté pan or griddle to medium-low heat. Spread butter on one side of each sandwich, then carefully place butter-side-down on the pan. Cook until golden brown, about 4 minutes. In the meantime, butter the top-facing side of bread, then flip and cook until golden on the other side.
Pro Tip: To melt the cheese, splash a little bit of water on the pan, then invert a large bowl over top to cover the sandwiches for one to two minutes. The water will evaporate and create steam, which will allow the cheese to melt.
- Transfer the sandwiches to a cutting board and use a serrated knife to slice them in half on a diagonal. Serve immediately.
Tips for Success
- Always toast over medium-low heat so the bread turns deep golden brown without burning and gives the cheese enough time to melt
- Use slices of sourdough bread or another sturdy bread to contain all the gooey cheeses.
- To help the cheese melt perfectly, splash a tablespoon of water on the bottom of the skillet and cover to trap steam.
Variations
- Swap the Swiss cheese for Gruyère, cheddar, fontina or even brie to go with the sweet caramelized onion.
- Make caramelized red onions for a pop of color.
- Stir in a bit of balsamic vinegar or beef stock or beef broth while cooking the onions for more flavor.
- Make it open-faced on broiled French bread.
- Add slices of steak or roast beef and serve with au jus for a French onion dip.
Serving Suggestions
Serve this sandwich with a crisp side salad or a cozy soup for a complete meal. Crispy oven baked Truffle Fries, potato chips or Beet Chips also make a great side. Or stick with the French theme and serve this creamy Celery Root Remoulade!
My Italian Potato and Green Bean Salad, a crunchy Vinegar Slaw or these easy quick Refrigerator Pickles are all great too!
How to Store and Reheat
Store leftover sandwiches in an airtight container in the refrigerator for up to 2 days. Reheat in a regular oven or toaster oven or air fryer until warm and crisp, or on the stovetop with a small splash of olive oil or butter. Avoid microwaving, as it can make the bread soggy.
FAQs
Yes. Caramelized onions can be made up to 5 days in advance and stored in an airtight container in the fridge. Reheat gently in a skillet before assembling your sandwiches.
Thick, sturdy slices like sourdough or French bread are ideal. They toast beautifully and hold up to the rich filling.
Cover the pan while toasting. The steam helps melt the cheese evenly without burning the buttery bread.
Absolutely. Up your cheese game with Gruyère cheese, Swiss cheese, Cheddar or even fontina melt perfectly and bring a rich flavor to your sandwich.
This sandwich pairs well with a fresh side salad, crispy fries, or a simple soup.
Did you LOVE this recipe? Please leave a star ⭐️ rating and comment and tag your creations @ColeyCooks on Instagram!
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French Onion Grilled Cheese Sandwich
Ingredients
- 2 tablespoons salted butter softened, plus more for the bread
- 2 medium yellow onions thinly sliced
- water as needed
- salt and pepper to taste
- ½ teaspoon fresh thyme leaves roughly chopped
- 1 teaspoon Worcestershire sauce
- 1 teaspoon sugar
- 1 teaspoon sherry vinegar or red wine vinegar
- 4 thick slices bread
- 6 slices Swiss cheese
Instructions
- Melt 2 tablespoons of butter in a large sauté pan over medium heat, then add the onions. Stir, then cover and cook until softened, about 5 minutes. Add a splash of water and scrape up any browned bits on the bottom, then cover and cook down some more. Repeat this process several more times until the onions have started to turn deep brown and caramelized.
- Add fresh thyme, Worcestershire sauce, sugar and vinegar, then season with salt and pepper to taste. Continue cooking for 2-3 more minutes, then transfer onions to a bowl.
- Spread a layer of onions on each slice of bread. Top two pieces of bread with a folded slice of Swiss cheese. Top with more onions, then another slice of cheese, then more onions, and one more slice of cheese. Place the remaining slices of bread on top and gently press down.
- Preheat a large saute pan or griddle to medium-low heat. Spread butter on one side of each sandwich, then carefully place butter-side-down on the pan. Cook until golden brown, about 4 minutes. In the meantime, butter the top-facing side of bread, then flip and cook until golden on the other side. To melt the cheese, splash a little bit of water on the pan, then invert a large bowl over top to cover the sandwiches for one to two minutes. The water will evaporate and create steam, which will allow the cheese to melt.
- Transfer the sandwiches to a cutting board and use a serrated knife to slice them in half on a diagonal. Serve immediately.
Notes
- To melt the cheese, splash a little bit of water on the pan, then invert a large bowl over top to cover the sandwiches for one to two minutes. The water will evaporate and create steam, which will allow the cheese to melt.
- Always toast over medium-low heat so the bread turns deep golden brown without burning and gives the cheese enough time to melt
- Use slices of sourdough bread or another sturdy bread to contain all the gooey cheeses.
- To help the cheese melt perfectly, splash a tablespoon of water on the bottom of the skillet and cover to trap steam.
Nutrition
OMG, what a great recipe! We really enjoyed this one!
Awesome! Glad you loved it!
Made your French Onion Grilled Cheese tonight for the family. Oh. My. This was exceptionally delicious! Our son actually exclaimed, "This is so good I could cry!" So definitely a keeper.
I prepared the onions as directed, but graded and blended a mix of Gruyere and Smoked Swiss cheese, used a San Francisco sourdough bread, and served with a side of lentil soup. The only thing I would do differently is make more onions!
Im so glad it was such a hit with you and your family! 🙂
This was the best grilled cheese ive ever fucking had holy shit that was wonderful
Awesome!! So glad you loved it!!
This literally looks amazing!!! I need to make this STAT!
THIS needs to happen, ASAP! My hubby and I just went to dinner and we ordered a french onion dip as appetizer..which basically was caramelized onions, cheese and toasted bread and we were enamored with how amazing it was. Funny, my hubby was like..oh we should make this into a grilled cheese (light bulb moment)...I kid you not, that was last week and now I see this!!
The difference between good French onion soup and mediocre French onion soup is staggering!! But why not just nix the liquid and get to the really good parts?? This grilled cheese is next level, stupid delicious. I used Trader Joe's thick sliced brioche and it's highly recommended! Nice and soft and just a teeny bit sweet. LMK if you make it!!
That is the most ooey gooey & perfectly golden grilled cheese I've ever laid eyes on.
Truer words have never been spoken!
Oh, you evil vixen. I can already feel the Pizza burn forming on the roof of my mouth since I know that I won't wait till it cools before I shove it down my face! I can already taste this blend of two of my favorite foods - French Onion soup and gooey grilled cheese. You should be ashamed! NOT!
Those comments and name calling are 100% warranted. I accept full responsibility. This grilled cheese is SO good. If you can get thick sliced brioche, even better.