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French onion grilled cheese cut in half

French Onion Grilled Cheese Sandwich

Chelsea Kram – XO&So: Vegetarian Comfort Food
You've never had a gourmet sandwich quite like this one. Inside, you'll find caramelized onions and white cheddar, then the very top of the sandwich gets a layer of bubbly, melted gruyere. The final result? A French onion grilled cheese that will change the way you think about sandwiches.
5 from 1 vote
Prep Time 10 mins
Cook Time 1 hr
Servings 2
Calories 1379 kcal


  • Cast-iron skillet


For the Caramelized Onions

  • 1 lb yellow onions about two large onions, peeled and cut into thin strips
  • 1 tbsp olive oil
  • 1 tbsp butter, unsalted
  • ½ tsp sugar
  • ¼ tsp salt
  • 2 cloves garlic chopped
  • 3 tbsp dry red wine I use malbec
  • cinnamon just a pinch!
  • black pepper

For the Grilled Cheese

  • 4 slices sourdough bread fresh, large slices
  • 4 tbsp unsalted butter* melted
  • tsp dried thyme
  • tsp dried rosemary
  • 7 oz white cheddar**, shredded or 4 slices of white cheddar
  • 3 oz gruyere*** shredded


For the Caramelized Onions

  • Heat the olive oil over medium heat in a large pan. When it's hot, add the sliced onions. Cook and stir often with a wooden spoon until the onions start to soften, about 20 minutes.
  • Add the butter and cook for another 20 minutes, continuing to stir every 2-4 minutes. Keep a close eye on your onions that they don't burn. Reduce heat if necessary.
  • Add the salt, sugar, cinnamon, and ground black pepper and continue cooking for another 15 minutes (this is when they'll really start to brown).
    Once you reach the 12 minute mark, add the chopped garlic.
  • Pour in the red wine to deglaze the pan. Using your wooden spoon, scrape the bottom and sides of the pan to get at any caramelized bits. Let cook for 2-3 minutes, or until the wine has mostly cooked off.
    Set the onions aside.

For the Grilled Cheese

  • Melt butter 4 tbsp. of butter a microwave-safe dish with a pinch each of rosemary and thyme (both or either). 
    Brush the melted butter onto one side of each slide of bread.
    a pinterest graphic showing a French onion grilled cheese
  • Place two slices butter-side-down into a cast iron skillet. Top both slices with the caramelized onions.
  • Add the shredded or sliced white cheddar on top of the onions.
  • Close the sandwiches using the other slices of bread, butter side up. 
    Place the skillet on medium heat, and cook for about 5-minutes, or until the bottom is golden and toasty.
    While the sandwiches cook, turn your oven to broil.
  • Once the bottom half of the bread is toasted in the pan, it's time to move your cast-iron skillet to the oven.****
    Let the sandwiches broil for a minute or two until the top piece of bread is golden and toasty.*****
  • Remove the skillet or sheet from the oven, and sprinkle the gruyere on top of the sandwiches.
    Return sandwiches to oven, and let cook for another minute or two, or until the cheese is golden and bubbly. 
  • Remove from the oven and cut in half. Sprinkle with more rosemary and thyme and serve hot.


*You likely won't use all of this butter, but it's better to have a bit left over than not use enough!
**Swiss will work too. 
***A mix of fontina and parmesan works well too. 
****(If you don't have a cast-iron skillet, you can use a regular pan to cook the first half. Then, move the sandwiches out of the pan and onto a baking sheet to go into the oven). 
*****(We cook it this way because it's very messy to flip these grilled cheese sandwiches because of all of their fillings!)


Calories: 1379kcalCarbohydrates: 98gProtein: 55gFat: 85gSaturated Fat: 49gCholesterol: 227mgSodium: 1769mgPotassium: 627mgFiber: 7gSugar: 15gVitamin A: 2282IUVitamin C: 18mgCalcium: 1266mgIron: 6mg
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