Name: French Onion Grilled Cheese Sandwich
Prep time: 10 min
Cook time: 45 min
Total time: 55 min
Ingredients: 2 large yellow onions (or sweet onions), peeled and sliced; 1 tablespoon olive oil; 3 tablespoons butter, plus more for buttering the bread; 1 teaspoon salt; 1/2 teaspoon black pepper; 1/2 teaspoon fresh thyme, chopped; 3 tablespoons white wine, beer, or beef stock; 1/2 cup Gruyere cheese, freshly grated; 1/4 cup Asiago cheese, freshly grated; 4 thick slices of sourdough or crusty bread

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Everything you love about French onion soup — the jammy onions, the melted cheese, the deep savory warmth — tucked between two buttered slices of crusty bread.

When old man winter arrives, I am all about warm comfort food. Most of the time that means a steamy bowl of soup. But some nights I want something a little easier and considerably cheesier — and that is when I make a French onion grilled cheese sandwich.

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This is one of and honestly it might be the best grilled cheese sandwich I have ever made. It takes everything that makes French onion soup worth standing over a stove for — the slow-cooked jammy onions, the deep golden brown caramelization, the rich cheesy pull — and puts it all between two slices of good bread. Perfect anytime. Even better on a cold, snowy night when you do not feel like making a full pot of soup.

I will tell you right now: I knew I was going to love this. So I made extra caramelized onions from the start. Half went into the sandwiches. The rest went into the refrigerator for later in the week — spooned into a batch of broccoli cheddar soup and, honestly, eaten standing at the counter with a spoon because I have no restraint where caramelized onions are concerned. Make extra. You will not regret it.

The Caramelized Onions — Worth Every Minute

Just like French onion soup, this sandwich lives or dies by the caramelized onions. The cooking process is slow and there is no shortcut worth taking. What you want at the end is a skillet full of deeply golden, jammy onions that smell like they have been cooking for a long time — because they have. That sweetness and depth is the whole point.

I use large yellow onions or sweet onions — both work beautifully here. Red onions are a lovely variation if you want something a little more savory and complex. A pinch of salt early in the process draws out the moisture and gets things moving. Some recipes add a tsp of sugar to nudge the caramelization along; I find the natural sweetness of yellow onions more than enough if you are patient.

Once your jammy onions are deeply golden and fragrant, deglaze the pan with a splash of white wine, beer, or beef stock — whatever you have. Scrape up every bit of those browned bits from the bottom of the skillet. That is pure flavor and it goes into the sandwich. I used beer when I made this, and the onions were absolutely scrumptious.

If you want to get ahead, caramelized onions keep beautifully in the refrigerator for up to a week. Make them on a Sunday and you are set. You can also make a large batch in a slow cooker overnight — low and slow with butter, onions, and a pinch of salt. Transfer onions to a jar when cool and you have a head start on the best grilled cheese sandwich of your week.

The Cheese — Do Not Skip Gruyere

I use a combination of Gruyere cheese and Asiago, and I want to make a case for grating your own. Pre-shredded cheese has fillers that prevent it from melting the way it should — what you want here is melted cheese that stretches and pulls and goes deep golden brown at the edges. Grate it yourself for best results.

Gruyere is the classic French onion soup cheese and it belongs here for the same reasons: nutty, rich, and it melts like a dream. Asiago adds a sharpness that keeps the whole sandwich from feeling one-note. Swiss cheese is a good substitution if Gruyere is hard to find — same family, similar melt.

The Bread — Go Crusty

This is not the sandwich for thin white sandwich bread. You want something with structure — thick slices of sourdough are ideal, or a good crusty country loaf. The bread needs to hold up to the weight of the caramelized onions and the melted cheese without going soggy. Butter both sides generously. The buttered sides hitting a hot griddle are what give you that deep golden brown crust.

What You Need

2 large yellow onions (or sweet onions), peeled and sliced
1 tablespoon olive oil
3 tablespoons butter, plus more for buttering the bread
1 teaspoon salt
1/2 teaspoon black pepper
1/2 teaspoon fresh thyme, chopped
3 tablespoons white wine, beer, or beef stock
1/2 cup Gruyere cheese, freshly grated
1/4 cup Asiago cheese, freshly grated
4 thick slices of sourdough or crusty bread

How to Make a French Onion Grilled Cheese Sandwich

In a large skillet over medium-high heat, melt the butter and olive oil together. When the butter melts and foams, add the sliced onions. Season with salt, pepper, and thyme. Spread the onions into an even layer and cover the pan.

Reduce heat to medium-low and let the onions steam for 10 to 15 minutes until softened. Remove the lid and continue cooking for another 25 minutes, stirring frequently, until the onions are jammy and deep golden brown. Do not rush this. Low and slow is the only way.

Once the onions are caramelized, add the white wine, beer, or beef stock to deglaze — scrape up all the browned bits from the bottom of the skillet. Those bits are flavor. Remove from heat and set aside.

Preheat a griddle or large skillet to medium-low heat. Butter both sides of each bread slice. Place one slice butter-side down and pile it with Gruyere cheese, Asiago, and a generous heap of caramelized onions. Top with the second slice of bread, butter side up.

Cover the sandwiches with a lid or an inverted bowl. Cook for 2 to 3 minutes until the bottom is golden brown, then flip carefully. Cover again and cook another 2 to 3 minutes until the cheese melts completely and both buttered sides are deep golden brown.

Move to a cutting board, cut on the diagonal, and serve immediately.

How to Serve It

This sandwich is a meal on its own. I serve it with potato chips — the crunch against all that melted cheese is just right. A simple side salad works beautifully if you want something green. And if you have any caramelized onions left, stir them into a bowl of French onion dip with sour cream for a little something on the side. Extraordinary.

A Few Variations

Add a smear of Dijon mustard on the bread before assembling — it wakes everything up.
A few fresh thyme leaves tucked in with the cheese adds an herby note that feels very French onion soup.
Bay leaves simmered with the onions during the steaming step add depth — remove before assembling.
Try it with red onions instead of yellow for a slightly more savory, complex flavor.
For a richer sandwich, swap the beef stock deglaze for a splash of white wine and add a thin cheese slice directly on the bread before the shredded cheese — a double layer of melted cheese is not a bad thing.

Are you a grilled cheese fan? This one takes a little more time than your standard cheese sandwich — mostly because of the onions — but it is absolutely worth it. The whole cooking process from start to finish is maybe 45 minutes, and most of that is the onions doing their thing while you do yours. Make extra onions. Keep them in the refrigerator. You will find yourself dreaming up other sandwiches all week, and I mean that as a promise, not a warning.

I would love to know: do you have a favorite cheese sandwich recipe? Leave a comment and tell me what you make on a cold night.

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