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.
This sandwich quickly became a favorite in my household for its perfect balance of sweet onions and melted cheese comfort.
Ingredients
- 2 tablespoons unsalted butter: for caramelizing onions and spreading on bread
- 2 large yellow onions, thinly sliced: the base of the caramelized onions
- 1 teaspoon sugar: enhances onion sweetness
- 1/2 teaspoon salt: seasoning for onions
- 1/4 teaspoon freshly ground black pepper: adds subtle spice
- 1 teaspoon fresh thyme leaves (or 1/2 teaspoon dried): herbs for flavor
- 1 tablespoon balsamic vinegar: adds depth
- 4 slices sourdough or country-style bread: sandwich base
- 2 tablespoons unsalted butter, softened: for spreading on bread
- 1 cup shredded Gruyère cheese: melty, savory cheese
- 1 cup shredded mozzarella cheese: adds creaminess
- 2 teaspoons Dijon mustard: tangy spread
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 My family loves enjoying these sandwiches together on cozy weekend afternoons.
Required Tools
Large skillet, spatula, bread knife, cheese grater
Allergen Information
Contains Milk (cheese, butter), Wheat (bread), Mustard. Check store-bought bread for additional allergens.
Nutritional Information
Per serving: Calories 540, Total Fat 32 g, Carbohydrates 44 g, Protein 22 g.
Save This sandwich is perfect comfort food elevated with simple ingredients and care.
Recipe FAQ
- → How do I caramelize onions properly?
Cook thinly sliced onions slowly in butter with sugar and salt over medium heat, stirring occasionally until they turn a deep golden brown and develop a sweet, rich flavor, usually about 25–30 minutes.
- → Which cheeses work best for melting?
Gruyère and mozzarella are excellent choices as they melt smoothly, combining creaminess with rich, nutty and mild flavors that complement the onions.
- → Can I use other breads besides sourdough?
Yes, country-style or similar sturdy breads work well, as they hold up during grilling and develop a crisp exterior while keeping the inside soft.
- → What does the Dijon mustard add?
The mustard adds a subtle tangy and slightly sharp note that enhances the overall flavor balance without overpowering the sandwich.
- → How do I get a perfectly grilled crust?
Butter the bread slices well and cook the sandwich over medium-low heat, pressing gently and flipping once, until golden brown and the cheese is melted, about 3-5 minutes per side.