French Onion Grilled Cheese Sandwiches

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Deeply caramelized onions and gooey Gruyère cheese take this soup-inspired sandwich over the top.

Active Time:
30 mins
Total Time:
1 hr
Yield:
4

If your favorite part of French onion soup is the gooey, cheesy crouton on top, this decadent grilled cheese is made for you. Inspired by the classic soup, former F&W food editor Grace Parisi makes this sandwich with sweet caramelized onions and nutty, savory Gruyère cheese. Whole-grain bread gets nice and toasty, while tangy Dijon mustard and pickle slices help to cut through the richness of all the butter and cheese. 

Frequently asked questions 

What is in French onion soup?

French onion soup is traditionally made with caramelized onions, beef broth, and a crouton that’s topped with melted Gruyère cheese. Its sweet and savory richness has inspired countless recipes beyond soup, including French Onion Pasta and French Onion Baked Brie.


What is Gruyère cheese?

Gruyère is a semi-hard yellow Swiss cheese made from whole cow’s milk that typically ages for three to six months. It has a savory, slightly nutty flavor and is known for its excellent meltability (it’s also a classic fondue cheese).

How do you make caramelized onions? 

Caramelized onions are made by slow-cooking onions in butter and/or oil until they take on a golden brown color, sweet flavor, and soft texture. Here, they’re cooked in a combination of oil and butter for about 40 minutes. Resist the urge to fast-track the process — a bit of patience is key to proper caramelized onions. You can use any onion, but yellow onions have a nice balance of sweetness and sharpness that makes them a traditional choice for French onion soup.

Notes from the Food & Wine Test Kitchen

Use a deep skillet when caramelizing the onions to prevent them from steaming. Make sure to scrape the bottom of the skillet when you’re stirring to keep the onions from scorching, and add water as needed to deglaze the skillet. When you’re cooking the grilled cheese, keep the heat low to ensure the bread doesn’t burn before the cheese melts. 

Make ahead

You can make the caramelized onions in advance. Let them cool, then store in an airtight container in the refrigerator for up to one week. Reheat gently in a skillet before layering on the bread. 

French Onion Grilled Cheese Sandwiches

Brie Goldman / Food Styling by Annie Prost / Prop Styling by Addelyn Evans

Ingredients

  • 3 tablespoons unsalted butter, softened

  • 1 tablespoon extra-virgin olive oil

  • 1 large onion, halved and thinly sliced crosswise (4 cups)

  • Salt and freshly ground pepper

  • Eight 1/2-inch-thick slices of whole-grain bread

  • Dijon mustard

  • 8 ounces Gruyère cheese, thinly sliced

  • 2 half-sour pickles, thinly sliced lengthwise

Directions

  1. In a deep skillet over medium-high, melt 1 tablespoon of the butter in the oil. Add onion, cover and cook, stirring once or twice, until softened, about 5 minutes. Uncover and cook over medium, stirring occasionally, until onion is very tender and caramelized, about 35 minutes longer. Add water to the skillet as necessary, 1/4 cup at a time, to prevent onion from scorching. Season caramelized onions with salt and pepper.

  2. Spread bread with the remaining 2 tablespoons of butter and arrange, buttered side down, on a work surface. Spread a thin layer of mustard on each slice. Top half of the slices with onion, Gruyère and pickles and close sandwiches.

  3. Preheat a skillet or panini press. Grill sandwiches over low heat until bread is toasted and cheese is melted, about 10 minutes. If using a skillet, press sandwiches with a spatula and flip them halfway through. Cut in half and serve right away.

Originally appeared: March 2008

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