Love french onion soup? I think you're going to love it even more in grilled cheese form! This French Onion Grilled Cheese takes perfectly caramelized onions and sandwiches them between two slices of buttery bread with fresh thyme and lots of melted gruyere cheese.

Head-on view of french onion grilled cheese sandwich halves stacked on each other with recipe title at top

(This recipe was originally published in August 2014, but was updated with new content and photos in 2021).

Today I put soup in a sandwich and am sharing the recipe with you now. OK, so I didn’t literally take a bowl of soup and spoon it into a sandwich.

But I did take my all-time favorite soup and combine it with my all-time favorite sandwich: French onion soup and the mighty grilled cheese sandwich.

When I was a kid, I would have eaten a bowl of french onion soup and a caesar salad every single night for dinner if I had the choice.

Every restaurant we went to, I eschewed the kids’ menu and asked to order two appetizers. My sodium-intake was probably out the roof, but I was happy.

I probably would have been even happier if that soup came in sandwich form. Because who on Earth chooses to eat a bowl of soup over a grilled cheese?

Oh, and I've already made it in pizza form!

How to Caramelize Onions

As with most grilled cheeses, this sandwich is easy to make. But it does require a little bit of time since caramelizing onions requires time.

And they're so, so worth it. Even if you think you don't like onions, I have a feeling that once you try them caramelized, you will be changing your tune. Especially if they're made into a grilled cheese!

To caramelize onions, start by placing a large skillet over medium heat and adding olive oil and 2 tablespoon butter.

Once butter is melted, add in onion slices, sprinkle with salt and pepper, and cook for about 5 minutes, stirring frequently.

It looks like a lot of onions for two sandwiches, but trust me, they are going to shrink down dramatically!

After 5 minutes, turn heat to low, add brown sugar and apple cider vinegar and stir occasionally as onions begin to brown.

Sliced onions in skillet partway through caramelizing process

Continue to cook and stir occasionally until onions are browned to your liking. Caramelization process will likely take at least 30 minutes total.

Before removing skillet from heat, stir in thyme.

Caramelized onions in skillet with chopped thyme mixed in

How to Make French Onion Grilled Cheese

Now that your onions are beautifully caramelized, you're ready to assemble your grilled cheese sandwiches.

Spread butter on one side of each bread slice.

Place a few slices of gruyere cheese on two of the bread slices (the unbuttered sides).

Pile caramelized onions on top of cheese.

Overhead view of slice of bread with gruyere cheese with caramelized onions on top

Add remaining cheese slices to the top of the onions.

Slice of bread with caramelized onions with gruyere cheese layered on top

Place remaining slices of bread on top, buttered sides facing out.

Heat a large skillet or griddle over medium-low heat (if you want to use the same skillet you just cooked the onions in, you can) and place sandwiches on skillet.

Head-on view of a french onion grilled cheese sandwich cooking on a skillet

Let cook for about 2 minutes before flipping sandwich and cooking for another 2 minutes on the other side, until bread is golden and cheese is melty.

Remove from skillet and slice sandwiches in half before serving.

Landscape head-on view of halves of a french onion grilled cheese sandwich stacked on each other

Like I said, even if you don't generally like onions, I implore you to try this sandwich!

My husband is one of those people who said he didn’t really want to try this because it involved so many onions.

Then he tried a bite and then had another. And another. And then a whole french onion grilled cheese was gone. Because nobody can resist caramelized onions!

Side view of a stack of french onion grilled cheese sandwich halves stacked on each other

If you’re still uncertain, combine them with slightly salty cheese and crispy bread and then come back and talk to me.

And if you're a fan of french onion soup? You are going to go absolutely wild for this grilled cheese sandwich!

It's like the soup with melty gruyere cheese is on the outside and the crispy buttery croutons are on the outside.

AKA my idea of heaven. Give me a side of Caesar salad and call it a meal my preteen self would order every single time she went out.

More Grilled Cheese Recipes

If you still don't think onions are your thing OR you just want more ways to enjoy grilled cheese (I could legit eat one every day), I have plenty of recipes for you.

Here are some of my favorite grilled cheese recipes:

Head-on view of french onion grilled cheese sandwich halves stacked on each other

We all know that grilled cheese is the perfect complement to soup... But now I can't stop thinking about more soups AS grilled cheese sandwiches.

And with that said... How do you think a chicken noodle soup sandwich would be?

What kind of soup would you love to eat in sandwich form?

📖 Recipe