Description
This French Onion Grilled Cheese recipe combines sweet, deeply caramelized onions with a flavorful blend of Gruyère and mozzarella cheeses, sandwiched between buttery, toasted slices of sourdough bread. Finished with a hint of thyme and tangy balsamic vinegar, and a touch of Dijon mustard for a sophisticated twist on the classic grilled cheese sandwich, it’s perfect for a comforting lunch or dinner.
Ingredients
Scale
Caramelized Onions
- 2 tablespoons unsalted butter
- 2 large yellow onions, thinly sliced
- 1 teaspoon granulated sugar
- 1/2 teaspoon salt
- 1/4 teaspoon freshly ground black pepper
- 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme
- 1 tablespoon balsamic vinegar
Sandwich
- 4 slices sourdough or country-style bread
- 2 tablespoons unsalted butter, softened
- 1 cup shredded Gruyère cheese (approximately 3.5 ounces)
- 1 cup shredded mozzarella cheese (approximately 3.5 ounces)
- 2 teaspoons Dijon mustard
Instructions
- Caramelize the Onions: In a large skillet over medium heat, melt 2 tablespoons of unsalted butter. Add the thinly sliced onions, granulated sugar, salt, and freshly ground black pepper. Cook the onions, stirring occasionally, until they become golden brown and deeply caramelized, which should take about 25 to 30 minutes.
- Finish the Onion Mixture: Stir in the fresh or dried thyme leaves along with 1 tablespoon of balsamic vinegar. Continue cooking for another 2 minutes until the mixture becomes fragrant. Remove the skillet from heat and set it aside.
- Prepare the Bread: Evenly butter one side of each slice of bread with the softened butter. Spread 2 teaspoons of Dijon mustard on the unbuttered side of two slices to add a tangy flavor layer.
- Assemble the Sandwiches: On the mustard-covered side of the bread, layer half of the shredded Gruyère and mozzarella cheeses evenly. Add a generous spoonful of the caramelized onion mixture over the cheese, then sprinkle the remaining cheese on top. Place the remaining slices of bread on top, ensuring the buttered sides face outward.
- Cook the Sandwiches: Preheat a clean skillet or griddle over medium-low heat. Place the assembled sandwiches on the skillet and cook for 3 to 5 minutes on each side, pressing gently and flipping once, until the bread is golden brown and the cheese is completely melted.
- Rest and Serve: Remove the sandwiches from the skillet and let them rest for 1 minute before slicing. Serve the sandwiches warm to enjoy the gooey cheese and savory caramelized onions at their best.
Notes
- For best results, use sourdough or country-style bread which holds up well to the fillings and frying.
- Cooking the onions low and slow is key to achieving rich, deep caramelization without burning.
- Feel free to substitute Gruyère with Swiss cheese or fontina if preferred.
- If you like extra flavor, add a pinch of smoked paprika or garlic powder to the onions while caramelizing.
- To make this recipe vegetarian, verify that your bread and mustard contain no animal-derived ingredients.
- Prep Time: 10 minutes
- Cook Time: 35 minutes
- Category: Sandwich
- Method: Frying
- Cuisine: French
Keywords: French onion grilled cheese, caramelized onion sandwich, Gruyère cheese sandwich, toasted cheese sandwich, savory grilled cheese
