This French Onion Grilled Cheese Sandwich with caramelized onions, melty Gruyere and toasty bread is wholesome comfort food! A tasty vegetarian meal, or make it vegan with vegan cheese!
Every once in a while, I get a hankering for a gooey, melty, toasty grilled cheese sandwich. They tick all the boxes for me as far as “comfort food,” and I often add other things besides cheese to jazz them up, like in our Caprese Grilled Cheese with summer tomatoes and arugula pesto or this Grilled Cheese with Cranberry Mustard and leftover Thanksgiving turkey.
But winter is here, and I crave umami depth, so I caramelized some onions and added them to the mix. Over the top delicious!
Why You’ll Love This
It’s so comforting! And sometimes I just need that. Flavorful, nutty Gruyere cheese is melted over onions that are caramelized long and slow, prepared like traditional French Onion Soup. Vegans can sub a melty vegan cheese!
Layers of delicious flavor! The process of caramelizing the onions brings out their delicious complexity and sweetness. I prefer to use a wholesome, homemade sourdough bread if possible, but in a pinch, store-bought French bread works great too.
Ingredients
- Onion: Use a large red onion, sweet onion, or yellow onion. These are the best for caramelizing!
- Gruyere cheese: We prefer to buy a block of cheese to grate, but you can use sliced gruyere too. To make vegan, sub a meltable vegan cheese.
- Hearty bread: Try our Sourdough Bread, or buy French bread or another rustic loaf.
- Butter and olive oil: Or use just olive oil. We like to use a mixture of unsalted butter and olive oil to bring the bread to golden-brown perfection.
- Sherry cooking wine (optional): Or use port, red-wine, or beef stock. You could also sub a splash of balsamic vinegar. For depth and complexity, infusing the onions with rich flavor.
- Fresh thyme (optional): For an especially woodsy, savory flavor that makes this grilled cheese perfect in winter.
- Whole grain mustard (optional): To give this grilled cheese a bit of sharp, pungent flavor that really elevates.
Buying Gruyère Cheese
Gruyere was always the cheese that was too expensive and luxurious to buy in my younger years. These days, I splurge on occasion, when I know it will make a real difference. You could substitute another cheese, and even make this vegan with all the good melty vegan cheeses available!
But I prefer Gruyere here – it’s earthy, complex and nutty, with the perfect balance of sweetness and saltiness, pairing perfectly with the caramelized onions.
For the full-flavored experience, splurge a little and try Gruyere. It will rock your world.
For this recipe, make sure to buy Gruyere that is young and softer, rather than aged… which will be hard with visible cracks.
How to Make French Onion Grilled Cheese
Step one: Warm olive oil over medium heat in a large skillet or cast iron pan. Add the sliced onion and stir, then reduce heat to medium-low. Sauté 20 minutes, stirring occasionally.
Step two: Once the onions sweat out their moisture and turn golden brown, add a generous pinch of kosher salt and a splash of sherry, port, or stock (optional), letting the liquid cook off—this is the essence of French onion soup! Turn off the heat, then remove the onions from the pan. Wipe with a paper towel to use again. Preheat the oven to 350F.
Step three: Spread the slices of sourdough (or French bread) with whole grain mustard (optional). On two slices, divide and layer the grated Gruyere, then add caramelized onions, sprinkle with fresh thyme leaves, and finally, add the rest of the cheese. Top with the other slice of bread and gently press together.
Step four: Bring the pan back to medium-low heat, then add the butter and olive oil. Place the sandwiches in the skillet and toast. Once the bread is golden brown and the cheese has begun to melt, carefully flip the sandwich to toast the other side.
Step five: If using an ovenproof skillet, simply place in the oven to fully melt the cheese. Otherwise you can transfer the sandwiches to a baking sheet. This prevents the bread from getting too dark.
Cut in half and enjoy immediately!
Chef’s Tips
- Grate the cheese. Freshly grated cheese is softer and melts more evenly, with a creamier consistency.
- Use an ovenproof skillet. This way you can simply place the pan straight into the oven to let the cheese melt without letting the bread get too dark.
- Use a combination of butter and olive oil. Butter adds rich, creamy flavor, while the oil prevents the bread from burning and turns the bread perfectly golden brown.
Storage
French Onion Grilled Cheese is best enjoyed right away, however you can store leftovers in the refrigerator for 2-3 days. Wrap tightly in plastic wrap to store. To reheat, place on a sheet pan in a 400F oven until warm all the way through, about 5-7 minutes.
Serving Suggestions
Serve this with a green salad, dressed with a light Dijon vinaigrette and enjoy the luscious flavors and textures!
FAQs
Gruyere is best! If you can’t find gruyere or want to try something else, comte, fontina, raclette, brie, or emmental can be used. Even swiss cheese or white cheddar could work.
Adding a little something extra beyond bread and cheese. Here we use caramelized onions! The whole grain mustard really elevates this too.
Finish them in the oven. Use an ovenproof skillet and get the bread golden-brown, then turn off the heat. Transfer the skillet to a 350F oven to finish melting the cheese.
Hope you love this delicious recipe as much as we do! Let me know what you think of the French Onion Grilled Cheese Sandwich in the comments!
xoxoxo
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French Onion Grilled Cheese Sandwich
- Prep Time: 15 mins
- Cook Time: 45 mins
- Total Time: 50 mins
- Yield: 2
- Category: Sandwich, vegetarian
- Method: Stovepot
- Cuisine: Northwest, vegetarian
- Diet: Vegetarian
Description
French onion Grilled Cheese Sandwich with caramelized onions and gruyere cheese. Serve with a salad for a delicious vegetarian dinner. Vegan adaptable.
Ingredients
- 1 large red, sweet or yellow onion- thinly sliced about 1/8 in thick
- 1–2 tablespoons olive oil
- generous pinch salt
- pinch fresh cracked pepper
- 1 tsp fresh thyme (optional)
- 1/4 cup sherry cooking wine, port, or beef stock (all optional, or sub a splash of balsamic vinegar)
- 4 slices hearty bread or French Bread
- 1 tablespoons butter ( or sub olive oil)
- 1 tablespoon olive oil
- 1 cup grated or sliced Gruyere cheese ( or meltable vegan cheese)
- Whole grain Mustard ( optional)
Instructions
- In a large heavy bottom skillet, or cast iron pan, heat oil over medium heat. Add onion and saute for 5 minutes, stirring to coat. Turn heat down to medium low. Stir occasionally and continue sauteing for 20 minutes.
- Onions will sweat out their moisture, and eventually caramelize into a beautiful deep golden brown. Add a generous pinch of salt, a splash of port, sherry, or stock (optional) and let the liquid cook off. Remove from pan and wipe it out with a paper towel, to use again. Preheat oven to 350 F
- Spread the bread with whole grain mustard (optional). On two slices, divide and layer shredded Gruyere, top with caramelized onions, sprinkle with fresh thyme leaves, then add the rest of the cheese. “Put the lid on” the sandwiches with the other slices of bread and gently press together
- Heat butter and olive oil in the same skillet over medium-low heat. Place sandwiches in the pan and toast, carefully flipping when perfectly golden brown and cheese begins to melt.
- Place in a warm oven to fully melt the cheese -which will preventing the bread from getting too dark. Cut in half and enjoy.
Nutrition
- Serving Size: ½ sandwich
- Calories: 520
- Sugar: 4.9 g
- Sodium: 1049.1 mg
- Fat: 22.5 g
- Saturated Fat: 9.5 g
- Carbohydrates: 58.5 g
- Fiber: 3.5 g
- Protein: 21.8 g
- Cholesterol: 43.9 mg
Really good sandwich. The flavors are great together. It’s easier to caramelize the onions in the oven. The heat will be more even and won’t tend to scorch the bottom. Also, do a few onion, at least. No point in going to the trouble to do just 1 onion.
Right, good advice, they are so nice to have on hand. I will have to try them in the oven! Glad you enjoyed the sandwich.
Hands down the best grilled cheese I’ve ever had. I think Gruyère cheese might be my new favorite! And I love the oven technique at the end, really gets it all so melty and delicious! Thank you for another amazing recipe!
Glad you enjoyed this Angeli!
Another wonderful recipe, with Once again, Sylvia’s special additions (that I’d never have thought of) make something simple, superb — grainy mustard on this? Masterful! Thank you, we’ll be eating these all winter!
Thanks Heidi!
Sylvia,
Did you try balsamic vinegar with the onions? Just curious.
I tried port and stock, but I’m thinking balsamic may be a good option, too? What do you think?
I think a splash of balsamic is a great idea!
Thank you!
I am a super fan of Sylvia. After emergency, life saving surgery this year, I wanted to find new and healthy recipes to protect and nourish my body. Her excellent and easy to prepare recipes have become a mainstay of our family meal planning. Thank you for your continued creativity. Good for you food that is a sheer joy to eat!! We love you!
Thanks so much and all the best on your health journey. ❤️
Loved it
Looks like just the thing for my vegetarian wife this Valentines Weekend – THANKS!
Was delicious, loved it ‼️
Me and my best friend are vegetarian and our favorite thing to do is grab a bottle of wine and cook dinner together. THESE WERE UNBELIEVABLY GOOD. We used a mixture of sweet yellow and red onion, spicy brown mustard, and a take and bake Italian loaf from Aldi. This was wildly better than I expected it to be (and I had super high hopes). Will be adding this to my personal cookbook to share for generations!
Awesome!
This was delicious! I forgot the thyme but it was fabulous anyway.
Amazing!! We’re new vegetarians and experimenting with lots of new recipes and this one is definitely a keeper. Its like french onion soup on a sandwich.
Great to hear!
“The smell alone, of Gruyere melting in your kitchen, is worth the extra expense. And can turn a grumpy husband into a kitten.”
Care to try switching up the genders and the adjectives and seeing if it still sounds just as cute?!?
Sorry, I see your point, this is just what happened to my husband.
I wish you would let people know that they can substitute vegan cheeses and it’ll be just as delicious. My favorite vegan cheeses are Violife mature cheddar slices, and Follow Your Heart smoked Gouda and provolone. You must know about the health hazards of dairy? And the cruelty of taking baby calves from mum? Thank you.
That is a great point Susan. At the time I made this recipe ( 2013) the vegan cheeses out there were not the best as far as melt-ability. Now they are meltable and tasty!
Thanks to Sylvia and her talent, this a wonderful site for food lovers and exchanging feedback on recipes – not a site to promote one’s views. Gruyère is a wonderful choice!
Yumm
Great to hear it Cindy!
Ok, I think died and went to heaven. Holy moly this was spectacular. Hubby loved it too and asked if we could have again tomorrow. 😉
This is hands down my favorite sandwich recipe. I didn’t like grilled cheese until I met this sandwich! It is fabulous.
Ahhh, funny! You are lucky–I unfortunately love all grilled cheese sandwiches!! But this one is one of my favs too!! Thanks for sharing!
This is just the best sandwich – family raved!
Yay, so glad you liked. We love it too!!
Love this grilled cheese recipe!
You had me at caramelized! Oh, and the Gruyere! I am melting! Thank you for the inspiration, recipe and beautiful photos!
A bowl of creamy celery soup or celeriac soup or parsnip soup goes great with they sandwich!
Onion soup in a sandwich! Delicious!
Completely beautiful – I’m battling some serious cravings now!
Cheese and onion one of my favorite combinations. Melted and caramelised brings on an even better combo. Make me one please.
anytime!
Those onions looks so amazing and sweet and caramelised and so delicious! My mouth is watering haha
http://youtube.com/addalittlefood
Those onions are total perfection. Yum!
A bowl of creamy celery soup or celeriac soup or parsnip soup goes great with the sandwich!
This looks so delicious. True, comfort food may not always be the healthiest, but it’s good for your SOUL. And as long as you’re using good ingredients (which you obviously are) the result will always be excellent!
I agree! Thanks.