Save to Pins A decadent twist on classic grilled cheese, this sandwich combines caramelized onions with gooey melted cheese for a deeply savory, next-level comfort food experience.
I love making this sandwich on chilly evenings when I want something simple yet indulgent that fills the kitchen with a wonderful aroma.
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Ingredients
- Caramelized Onions: 2 tablespoons unsalted butter, 2 large yellow onions thinly sliced, 1 teaspoon sugar, 1/2 teaspoon salt, 1/4 teaspoon freshly ground black pepper, 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried, 1 tablespoon balsamic vinegar
- Sandwich: 4 slices sourdough or country-style bread, 2 tablespoons unsalted butter softened, 1 cup (about 100 g) shredded Gruyère cheese, 1 cup (about 100 g) shredded mozzarella cheese, 2 teaspoons Dijon mustard
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Instructions
- Step 1:
- Melt 2 tablespoons butter in a large skillet over medium heat. Add sliced onions, sugar, salt, and pepper. Cook, stirring occasionally, until onions are golden brown and deeply caramelized, about 25 30 minutes.
- Step 2:
- Stir in thyme and balsamic vinegar cook another 2 minutes until fragrant. Remove from heat and set aside.
- Step 3:
- Butter one side of each bread slice. Spread Dijon mustard on the unbuttered side of two slices.
- Step 4:
- Layer half the Gruyère and mozzarella onto the mustard side. Top with a generous spoonful of caramelized onions, then the remaining cheese. Place the other bread slices on top, buttered side facing out.
- Step 5:
- Heat a clean skillet or griddle over medium-low heat. Cook sandwiches 3 5 minutes per side, pressing gently and flipping once, until bread is golden and cheese is fully melted.
- Step 6:
- Let rest 1 minute before slicing. Serve hot.
Save to Pins My family gathers around the table eagerly whenever I make this sandwich; it never lasts long!
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Required Tools
Large skillet, spatula, bread knife, cheese grater
Allergen Information
Contains Milk (cheese butter), Wheat (bread), Mustard. If using store-bought bread, check for additional allergens.
Nutritional Information
Calories 540, Total Fat 32 g, Carbohydrates 44 g, Protein 22 g per serving
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This sandwich is best enjoyed fresh and hot with a side of soup or salad for a complete meal.
Questions & Answers
- → How do I properly caramelize the onions?
Cook thinly sliced onions slowly in butter over medium heat, stirring occasionally, until they turn golden brown and soft, about 25–30 minutes. Adding sugar helps enhance the caramelization.
- → Can I substitute the Gruyère cheese?
Yes, cheeses like Comté or Swiss work well as alternatives, offering similar melting qualities and flavor profiles.
- → What bread type is best for this sandwich?
Sourdough or country-style bread with a sturdy texture helps hold the fillings and crisps nicely when grilled.
- → Why add Dijon mustard on the sandwich?
Dijon mustard adds a subtle tang that complements the sweetness of caramelized onions and the richness of melted cheeses.
- → How long should I grill the sandwich?
Grill each side over medium-low heat for 3–5 minutes until the bread is golden brown and the cheese has fully melted.
