Save 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.
Ingredients
- For the 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
- For the 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
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 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
Save Cooking Questions & Answers
- → How do I caramelize onions properly?
Cook sliced onions slowly in butter over medium heat, stirring occasionally until they're golden brown and soft, usually around 25-30 minutes, to develop deep sweetness.
- → What cheeses work best for melting in this sandwich?
Gruyère and mozzarella offer creamy melts and mild nuttiness, but Comté or Swiss cheese can be excellent substitutes for similar texture and flavor.
- → Can I prepare the caramelized onions ahead of time?
Yes, onions can be caramelized in advance and stored refrigerated for up to 3 days, which saves time when assembling the sandwich later.
- → What type of bread enhances the sandwich’s flavor?
Sourdough or country-style bread provides a sturdy, tangy base that crisps well when buttered and grilled, complementing the rich filling.
- → Are there ways to add extra flavor to the onions?
Adding a splash of balsamic vinegar or dry white wine towards the end of cooking heightens the onions’ complexity, balancing sweetness with acidity.