This French Onion Grilled Cheese is cheesy, toasty perfection with a rich, sweet onion twist. All the flavor of soup, but you can eat it with your hands. Win-win.
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You know that moment when you want French onion soup but don’t want to dirty a soup pot, a broiler, and half your kitchen? Enter: French Onion Grilled Cheese. It’s gooey, toasty, oniony perfection, basically the lovechild of the grilled cheese your mom made you as a kid and the fancy soup you order at a nice restaurant.
I love making this when I have girlfriends over because it feels nostalgic (grilled cheese night, anyone?) but dressed up enough that we can pair it with a glass of red-wine and call it dinner.
Why You’ll Love French Onion Grilled Cheese
- Caramelized onions = magic. Yes, they take a little time, but they’re the main character of this sandwich.
- Two cheeses are better than one. Gruyere brings the fancy vibes, mozzarella brings the stretch. Together? A match made in melty-cheese heaven.
- It’s comfort food, upgraded. Perfect for cozy nights, impressing guests, or just treating yourself because you survived a Monday.
Before You Start: Tips & Ingredients
- Onions – Slice them thin and take your time because they’re about to become golden and have an amazing rich flavor. This is not the time to rush. You’re aiming for deep golden brown and sweet, not “oops, I made onion charcoal.” Low and slow wins.
(Yellow onion makes the best caramelized onions – thanks to their natural sugars). - Butter + olive oil – Flavor and insurance against burnt onions.
- Beef broth – Deglazes the pan so you get every bit of flavor (water works too, but broth says “I care”).
- Cheese – Gruyere is classic, but Swiss or mozzarella will happily step in. You will not be disappointed with the cheese melt.
- Bread – 2 slices of Sourdough is ideal because it’s sturdy enough to hold all the gooey goodness.
- Optional extras – Dijon mustard for a little zing, garlic rub for drama or throw in some cognac in with the onions for that classic French onion soup taste
Substitutions
- Onions: Yellow onions are best for caramelized onions, but you can substitute white or sweet onions will still bring plenty of rich flavor.
- Cheese: Gruyere is classic, but Swiss, provolone, or even sharp cheddar work if that’s what’s in your fridge.
- Bread: Sourdough bread holds up beautifully, but any sturdy bread (like French bread or ciabatta) makes a solid stand-in.
- Butter: Swap with mayonnaise on the outside of the bread for that extra crunch.
- Beef broth: Vegetable or chicken broth, or even water, will deglaze the pan just fine.
- Dijon mustard: Leave it out if you’re not a mustard fan, or replace with a swipe of mayo or hot sauce for a different twist.
Frequently Asked Questions
You can, but be warned: slices of sourdough are sturdier and less likely to collapse under the weight of molten cheese + onions.
Yes. The grilled cheese council (aka me) insists on maximum goo.
Not really. But you can pour a glass of wine, scroll Instagram, or practice your “cheese pull” face while you wait.
Absolutely! Use a 9×13-inch pan and add 5–10 minutes to the bake time.
Leftovers? Bold of you to assume there will be leftovers. But yes, you can tuck them into the fridge for up to 2 days. Just know the bread will lose a bit of its crisp, so reheat it in a skillet (not the microwave) to bring the crunch back.
This French Onion Grilled Cheese Recipe is melty, cheesy, and just bougie enough to make you feel like you’ve got your life together. Serve it with a simple salad or just go full girl dinner and have it with a glass of red-wine and lots of paper towel.
Try These Recipes Next
- Buffalo Ranch Chicken Pot Pie
- Beer Cheese Dip
- Cheesy Sausage Stuffed Mushrooms
- Over-the-Top Triple Cheese Mac and Cheese
- Chili Garlic Beef Noodles
French Onion Grilled Cheese
Ingredients
- 2 tablespoons butter , divided
- 1 tablespoon olive oil
- 1 large onion , thinly sliced
- ½ teaspoon salt
- ½ teaspoon black pepper
- ½ teaspoon sugar
- ½ teaspoon fresh thyme leaves , or ¼ teaspoon dried
- 2 tablespoons beef broth low sodium, or water
- 4 slices sourdough bread
- 1 cup Gruyère cheese , shredded, or Swiss
- ½ cup mozzarella cheese , shredded
- 1 teaspoon Dijon mustard , optional, for extra depth
- 1 clove garlic , halved, for rubbing the bread
Instructions
- Melt 1 tablespoon butter with olive oil in a skillet over medium-low heat. Add the onions, salt, pepper, sugar, and thyme. Cook, stirring occasionally, for 15–20 minutes until golden and soft. Add the beef broth and stir to deglaze the pan, cooking until absorbed. Remove from heat.
- Butter one side of each bread slice. On the unbuttered side, spread Dijon mustard (if using), then layer half the shredded cheeses and the caramelized onions. Top with the remaining cheese and a slice of bread, buttered side facing out.
- Heat a clean skillet over medium-low heat. Cook each sandwich for about 3–4 minutes per side, pressing slightly with a spatula, until golden brown and the cheese is melted.
- Rub the toasted bread lightly with the cut side of the garlic clove for extra flavor. Slice in half and serve immediately!
Recipe Notes
- Low and slow. Caramelize those onions gently, rushing them means losing that deep, sweet flavor.
- Gruyère is king. Swiss works too, but Gruyère brings that nutty, luxurious flavor that makes this sandwich unforgettable.
- Rubbing with garlic = magic. It’s a tiny step that adds big flavor, so don’t skip it.
- Cheese layering matters. Put cheese on both sides of the onions so it melts evenly and holds the sandwich together.
- Serve immediately. Like all grilled cheese, this is best piping hot and fresh off the pan.
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