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French Onion Grilled Cheese Sandwich Recipe
Ben Carraoli

French Onion Grilled Cheese Sandwich Recipe

I recently made this French Onion Grilled Cheese Sandwich, and I can’t stop thinking about it. The moment those onions started caramelizing, my whole kitchen smelled cozy and comforting. When I layered in the cheese and grilled everything until golden and melty, it felt like making a warm hug on a plate.
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Prep Time 15 minutes
Cook Time 45 minutes
Ingredients Method Notes

Ingredients
  

  • 1 large red sweet, or yellow onion, thinly sliced (they caramelize beautifully and bring deep flavor)
  • 1 –2 tablespoons olive oil helps soften and brown the onions slowly
  • A generous pinch of kosher salt brings out the onions’ natural sweetness
  • Freshly cracked black pepper to taste (adds subtle heat)
  • 1 teaspoon fresh thyme optional (adds earthy, herb flavor)
  • ¼ cup sherry cooking wine port, beef stock, or a splash of balsamic vinegar (for deglazing and depth)
  • 4 slices hearty or rustic bread sturdy enough to hold the filling
  • 1 tablespoon butter or olive oil for crisping the sandwich
  • 1 tablespoon olive oil additional, for grilling
  • 1 cup grated or sliced Gruyère cheese or meltable vegan cheese melts smoothly and adds nutty richness
  • Whole grain mustard optional (for a tangy contrast)

Method
 

  1. Warm the olive oil in a skillet over medium heat, then add the sliced onions. Stir occasionally and reduce the heat to medium-low. Let them soften and caramelize slowly for about 20 minutes until golden and fragrant.
  2. Once caramelized, sprinkle in salt and pour in the sherry, stock, or balsamic. This loosens the browned bits and intensifies the flavor. When the liquid cooks off, stir in thyme and remove the onions from the heat.
  3. Lay out your bread slices. Spread mustard if you’re using it. Add half the cheese to one slice, spoon on the caramelized onions, add thyme if desired, then top with the rest of the cheese and the second bread slice.
  4. Heat butter and olive oil in the pan over medium-low heat. Place the sandwich in and cook until the bread turns golden brown. Flip carefully and cook the other side. For extra meltiness, place the skillet in a 350°F oven for a few minutes to finish.

Notes

I always grate cheese fresh — it melts smoother and tastes richer.
I never rush the onions; slow cooking makes them sweet and jammy.
I grill using both butter and olive oil because the combo gives flavor and prevents burning.
I often make the onions ahead since they store so well.
I preheat the skillet before adding the sandwich — it helps create a perfect crust.