French onion grilled cheese is the best of both worlds: French onion soup AND grilled cheese. This way, you don't have to choose one over the other for dinner - it's like a fancier, grown-up grilled cheese sandwich. The caramelized onions are cooked low and slow, creating a melty, gooey, and rich sandwich.
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One of my favorite ways to make a grilled cheese sandwich is by adding caramelized onions and turning it into a French onion grilled cheese (very similar to a British cheese and onion toastie).
The caramelized onions are cooked low and slow, and a slight tanginess is provided by white wine vinegar, which helps to cut the richness of Gruyère and creamy Swiss cheese.
Tangy sourdough marries all of the flavors and holds up well against this delightfully gooey mess of a sandwich. Serve it with vegetarian white bean chili or cucumber gazpacho for a hearty meal!
Jump to:
- ⭐️ Why This Grilled Cheese Recipe is the Best
- 🤔 What is the Secret to the Best Grilled Cheese?
- 🌿 Ingredient Notes
- 📝 Variations & Substitutions
- 🔪 How To Make Caramelized Onion Grilled Cheese
- 👩🏼🍳 Expert Tips
- 🍽 How to Serve Grilled Cheese with Caramelized Onions
- 💬 Frequently Asked Questions
- 🥪 More Sandwich Recipes
- French Onion Grilled Cheese (with Caramelized Onion)
⭐️ Why This Grilled Cheese Recipe is the Best
- Melty, gooey, rich, and toasty sourdough grilled cheese
- Easy weeknight dinner or more indulgent weekend treat
- Vegetarian comfort food
- Budget-friendly recipe
- Cheesy, buttery, slightly sweet, and tangy French onion soup grilled cheese
🤔 What is the Secret to the Best Grilled Cheese?
When it comes to making the best grilled cheese sandwich, it's all about achieving that perfect balance of crispy, golden-brown exterior and gooey, melty interior.
First, choose a high-quality, slightly thick-sliced bread. Next, use a generous amount of butter on each slice, as that's what gives it that coveted crunch and rich flavor. Another key is using two different types of cheese. This can take your grilled cheese to the next level.
Finally, don't rush the cooking process. Slow and steady wins the race here! Cook your sandwich over medium-low heat, giving it enough time to become beautifully golden on the outside while allowing the cheese to melt into a creamy, luscious filling. Remember, patience is key to mastering the art of the best grilled cheese.
🌿 Ingredient Notes
- Unsalted butter - Smearing your bread with butter makes for a golden (and much richer) grilled cheese. I recommend using unsalted butter to control the amount of salt used. If you only have salted butter on hand, skip the added salt.
- Yellow onion - The star of this sandwich. Make sure you go low and slow when caramelizing your onion. If you love caramelized onions like I do, don't miss my caramelized shallot pasta!
- Fresh thyme leaves and garlic - Adds lovely aromatics to our grilled cheese with onions.
- White wine vinegar - Cuts through the richness of the cheese and adds a slight zippy note.
- Gruyère cheese - A nutty, salty, and earthy cheese that's key to French onion soup. Make sure to avoid pre-grated cheese, as it will not melt as well as a block of cheese that you grate yourself.
- Swiss cheese - A milder, softer cheese that melts really well.
- Sourdough bread - Use high-quality sourdough (or your favorite loaf of bread) for this cheese and onion sandwich. It really makes a difference.
📝 Variations & Substitutions
- Use red onion for a slightly different flavor profile.
- Vinegar. Substituting red wine vinegar or apple cider vinegar will work nicely in place of the white wine vinegar.
- Use mayonnaise in place of butter to slather your bread before toasting. It may sound strange, but some people swear by it! Using mayo adds more tanginess and richness to your grilled cheese sandwich.
🔪 How To Make Caramelized Onion Grilled Cheese
Caramelize onions: Over medium heat, melt 2 tablespoons of butter in a large frying pan. Add sliced onion and adjust heat to medium-low. Cook until onion is soft and brown, around 30 minutes, stirring every once in a while.
Add thyme, garlic, salt, and white wine vinegar, and cook for an additional 2 minutes. Transfer onions to a bowl.
Use a paper towel to wipe out the skillet. Then, adjust heat to low and add remaining 2 tablespoons of butter to pan. Place two slices of sourdough in pan, and distribute cheese evenly over both slices of sourdough. Add caramelized onion mixture and place remaining 2 slices of sourdough on top.
Cook on one side until golden brown, 5-6 minutes, then flip and cook other side for another 3-4 minutes. Remove from pan and cut in half. Serve immediately.
👩🏼🍳 Expert Tips
- Go low and slow. When caramelizing onions, be sure to use a low heat setting. You don't want to fry the onions, but instead transform them into silky, soft onions that become slightly sweet.
- Use high-quality bread. I love the slight tang of sourdough, but use whatever your favorite loaf of bread is. Treat yourself to a nice loaf from your local bakery - it's worth it for this toasted sandwich.
- How to store: Wrap grilled cheese in foil and store in the refrigerator for up to 4 days; follow reheating instructions below.
- To reheat: Use your toaster oven (or regular oven) for best results. I recommend reheating for about 10 minutes at 350 degrees F. Microwaving your sandwich may lead to soggy bread, which would not be pleasant!
- Make in oven: Heat oil or butter in a large ovenproof skillet over medium heat. Toast both sides of bread until golden brown. Place in a 350 degree F. oven until cheese is melted and gooey.
- Avoid pre-grated cheese. Try to avoid pre-grated (shredded) cheese, as it includes additives that prevent it from melting nicely.
🍽 How to Serve Grilled Cheese with Caramelized Onions
Pair your homemade grilled cheese sandwich with a side of vegetables, like roasted carrots and green beans
Serve it with a side salad, like citrus fennel salad or cabbage slaw
Pair it with a hearty cup of soup, like chickpea soup
Serve it with a savory dipping sauce, like Sriracha garlic sauce, for a spicy kick
💬 Frequently Asked Questions
Since French onion soup is classically made with Swiss cheese and/or Gruyère, I wouldn't recommend using a different type of cheese. That said, all cheese is delicious so any substitution will work!
You can use either butter or vegetable oil to make a delicious grilled cheese, but the texture and flavor will be different. If you use vegetable oil, your sandwich will be slightly crispier but it will be missing that rich buttery flavor that is synonymous with grilled cheese sandwiches.
One important factor is to avoid pre-grated cheese, which doesn't have the best melting capabilities. Another pro-tip is to cook your grilled cheese over low heat. This gives the cheese time to melt without burning the bread.
🥪 More Sandwich Recipes
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French Onion Grilled Cheese (with Caramelized Onion)
Ingredients
- 4 Tablespoons unsalted butter
- 1 yellow onion, sliced into half moons
- 2 sprigs fresh thyme leaves
- 1 clove garlic, minced
- ½ teaspoon salt
- ¼ teaspoon black pepper
- 1 Tablespoon white wine vinegar
- 2 ounces Gruyère (about 3 slices)
- 2 ounces Swiss cheese (about 3 slices)
- 4 slices sourdough bread
Instructions
- Over medium heat, melt 2 tablespoons butter in a large frying pan. Add sliced onion and adjust heat to medium-low. Cook until onion is soft and brown, around 30 minutes, stirring every once in a while.
- Add thyme, garlic, salt, pepper, and white wine vinegar, and cook for an additional 2 minutes. Transfer onions to a bowl.
- Use a paper towel to wipe out skillet. Then, adjust heat to low and add remaining 2 tablespoons of butter to pan. Place two slices of sourdough in pan, and distribute cheese evenly over both slices of sourdough. Add onion mixture and place remaining 2 slices of sourdough on top.
- Cook on one side until golden brown, 5-6 minutes, then flip and cook other side for another 3-4 minutes. Remove from pan and cut in half. Serve immediately.
Video
Notes
-
- Go low and slow. When caramelizing onions, be sure to use a low heat setting. You don't want to fry the onions, but instead transform them into silky, soft onions that become slightly sweet.
-
- Use high-quality bread. I love the slight tang of sourdough, but use whatever your favorite loaf of bread is. Treat yourself to a nice loaf from your local bakery - it's worth it for this toasted sandwich.
-
- How to store: Wrap grilled cheese in foil and store in the refrigerator for up to 4 days; follow reheating instructions below.
-
- Avoid pre-grated cheese. Try to avoid pre-grated (shredded) cheese, as it includes additives that prevent it from melting nicely.
Oscar
oh my gosh. Two of my favourite things. French onion soup and grilled cheese sandwiches. This was so good, will be making this again soon.
Gastronotherapy
Thanks, Oscar!
Andrea
Wow! What an incredible sandwich. Love that you use gruyere and swiss as they go best with the french onions.
Gastronotherapy
Thanks, Andrea! Yes, I LOVE Gruyère!
rebecca
WOW!!! Not sure why I haven't thought of this before, but adding caramelized onions with all the delicious french onion flavors-holy yum! thanks for the great idea
Gastronotherapy
Yes, it's a super delicious combo!
Kate
Whoa, two amazing things in one grilled sandwich - I didn't think grilled cheese could get much better but this blew my mind!
Gastronotherapy
Thanks, Kate!
Ramona
This sandwich looks absolutely incredible, I’m just going to go make make one and replaced the cheese since I don’t have the gruyere. Oh, I’m so hungry now.
Gastronotherapy
Thanks, Ramona! I hope your sandwich was tasty! 😉
Bonnie
I'd love to know what cheese you substituted...I've never tried Gruyere cheese and am unsure if using it.
Gastronotherapy
Hi Bonnie, Gruyère is a Swiss cheese with a nutty flavor to it. It's one of my favorite cheeses! But, if you aren't up for trying it, you could stick with just the Swiss cheese and maybe add some Parmesan to get a similarly nutty flavor. Let me know if you try it, and thanks for stopping by!
Nathan
Anything involving onion already has my attention, so this French onion grilled cheese just sounds absolutely PERFECT. Great cheese combination too, can't wait to try this one!!
Gastronotherapy
Thanks, Nathan! If you like onions, you will love this sandwich! 🙂
Nora
This looks so delicious and the seasoning sounds wonderful! Can't wait to try this one!
michele
Love love the combo of cheeses and thyme in this sandwich.
Gastronotherapy
Thanks, Michele! 🙂
Genevieve
Oh my does this look delicious or what? I need this grilled cheese in my life!
Gastronotherapy
Thanks, Genevieve! 🙂
Alice | SkinnySpatula
Wow, this looks so good. Absolutely love that you added thyme to this grilled cheese sandwich.
Gastronotherapy
Thanks, Alice!
Katie Youngs
This sounds sooooo good!
Gastronotherapy
Thanks, Katie! 🙂
Barbara J Haner
This will be my next Sunday brunch menu item! Sounds and looks so good!!
Gastronotherapy
This would be perfect for Sunday brunch!