French Onion Grilled Cheese

French onion soup and grilled cheese are two classic recipes that really don’t need any tweaking. In fact, some may even consider it sacrilegious to modify or deviate from the originals. But as we’ve learned from our comfort food mashup recipes, sometimes marrying two old-fashioned favorites can lead to a creation that’s even more loveable than the original—and that’s certainly the case with this French onion grilled cheese sandwich.

This ooey-gooey wonder isn’t your average grilled cheese made with cellophane-wrapped American cheese. Instead, it’s made with aged Swiss and Gruyere cheeses and layered with a flavor-packed mixture of caramelized onions, herbs and jus. It has all the rich, savory flavors of a steaming crock of French onion soup but in handheld form. The creation is a truly divine experience.

What we love most about this sandwich is that it can satisfy a craving for the classic soup in a fraction of the time. Traditional French onion soup is made by slowly caramelizing the onions to release their sugars and develop the soup’s deep flavor, but this French onion recipe uses a few handy shortcuts to cut the cooking time down to about 30 minutes. Dreams really can come true!

Ingredients for French Onion Grilled Cheese

• Yellow onions: Of all the type of onions, we love using yellow onions in French onion soup recipes because they have the perfect combination of zip and sweetness.
• Olive oil and butter: A combination of oil and butter is ideal for caramelizing onions. The butter adds richness and flavor, while oil offers a higher smoke point, which allows the onions to cook at a higher temperature without burning.
• Dried herbs: A trio of dried thyme, rosemary and bay leaves infuses the onions with wonderful earthy flavors and woodsy aromas.
• Black pepper: A bit of black pepper adds bite to the onion mixture.
• Brown sugar: Brown sugar helps the onions brown faster and adds sweetness.
• Jus mix: This is our secret ingredient for giving the onions a rich, beefy umami flavor.
• Parmesan cheese: Mixing Parmesan into the butter develops an extra-crisp, cheesy crust on the bread as it cooks, reminiscent of the cheesy crouton in this slow-cooker French onion soup.
• Sourdough bread: We love the tangy flavor of sourdough for this sandwich, but it isn’t your only option. Any sturdy bread will do. Just avoid those that are overly soft. The onions add a lot of moisture to the sandwiches, so a denser artisan-style loaf is your best bet.
• Swiss and Gruyere: This duo of cheeses is classic for French onion soup, so it’s an obvious choice for the French onion grilled cheeses. For best results, grate the cheese by hand from the block so it melts smoothly.

Directions

Step 1: Caramelize the onions

In a large skillet, heat 1 tablespoon of butter with 1 tablespoon of olive oil. Add the thinly sliced onions, dried thyme, dried rosemary, bay leaf, pepper and brown sugar. Cover the skillet and cook the onions over medium-low heat for 15 to 20 minutes, stirring occasionally, until the onions are soft and lightly browned.

Editor’s Tip: You could also use the slow cooker to caramelize onions if you want less hands-on time with this sweet onion recipe.

Step 2: Mix the Parmesan butter

Meanwhile, mix the Parmesan cheese with the remaining softened butter. Set aside.

Step 3: Add the jus

Uncover the onions and increase the heat to medium. Add the water and jus mix, then simmer until it’s reduced, two to three minutes. Remove the pan from the heat and discard the bay leaf.

Step 4: Assemble the sandwiches

Preheat a large nonstick skillet or griddle over medium heat. Top half the slices of bread with two slices of Swiss cheese, followed by a third of the caramelized onions. Sprinkle each with 1/4 cup of Gruyere, then top with another slice of bread.

Spread the Parmesan butter evenly on both sides of the sandwiches.

Step 5: Toast until golden

Place the sandwiches on the preheated griddle. Cook them until they’re golden brown and the cheese is melted, three to four minutes per side. Transfer them to a cutting board and cut each sandwich in half. Serve them warm.

French Onion Grilled Cheese Variations

• Add bacon: This five-star bacon grilled cheese gets glowing reviews, so we bet a bacon French onion grilled cheese would be equally magical. Add two to three strips of crispy, cooked bacon to each sandwich as you assemble them.
• Add chicken or steak: For a protein boost, layer strips of grilled chicken or thinly shaved steak on the sandwiches.
• Swap for mayo: Using mayonnaise on grilled cheese is a sandwich-making secret you should know. It crisps up the bread very nicely for hot sandwiches. To use this trick in this recipe, mix the Parmesan cheese with mayo rather than butter, then spread it over the bread before toasting the sandwiches.
• More cheese options: If you don’t want to splurge on Gruyere or can’t find it at your supermarket, you can use exclusively Swiss cheese. Otherwise, provolone, fontina or Emmenthaler cheese are other suitable swaps.

How to Store French Onion Grilled Cheese

A French onion grilled cheese is best enjoyed fresh and hot from a griddle. If you need to store a portion of the sandwich as leftovers, place it in an airtight food storage container and refrigerate it. It will last up to four days, but is best enjoyed within one or two days.

How can you reheat a French onion grilled cheese?

To reheat a grilled cheese, avoid using a microwave as the bread will become soggy. For best results, warm a skillet over medium heat on the stovetop. Add the sandwich and cover it with a lid. Cook it for two to three minutes, then uncover the pan and flip the sandwich. Cook it for an additional two to three minutes on the other side until the cheese is melted and the bread is crisp.

French Onion Grilled Cheese Tips

How do you make caramelized onions on the stove top?

Traditionally, you want to cook the thinly sliced onions slowly over low heat in a bit of butter and/or olive oil. Using gentle heat over a long duration (usually 45 to 60 minutes) draws out their sugars, yielding onions with a deep, sweet flavor. The reason our onions cook faster is because we add the jus packet and water to speed up the flavoring and browning process.

What else can you do with caramelized onions?

If you have extra caramelized onions, save them in an airtight food storage container and refrigerate them for up to four days. To enjoy, add them to a frittata or to a juicy mushroom and Swiss burger. Reheat the onions in the microwave until they’re warm before using them.

What can you serve with a French onion grilled cheese?

Serve this French onion grilled cheese sandwich with a batch of homemade French fries or crunchy baked potato chips. For lighter fare, pair it with a garden salad or a cup of creamy chicken and wild rice soup.