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This indulgent sandwich captures everything you love about French onion soup—caramelized onions, gooey melted cheese, buttery crisp bread—and packs it between slices of golden, griddled perfection. Rich, savory, and incredibly satisfying.

🍴 Ingredients

• 2 tablespoons butter
• 1 tablespoon olive oil
• 2 large yellow onions, thinly sliced
• 1/2 teaspoon sugar
• 1/4 teaspoon salt
• 1/2 teaspoon fresh thyme leaves (optional)
• 4 slices crusty bread (like sourdough or rustic Italian)
• 1 cup shredded Gruyère cheese (or Swiss as a substitute)
• 1/2 cup shredded mozzarella (optional, for extra meltiness)
• 2 teaspoons Dijon mustard (optional)
• Extra butter, for grilling

🔥 Instructions

Caramelize the Onions:
In a skillet over medium heat, melt the butter and olive oil. Add sliced onions, sugar, and salt. Cook slowly, stirring often, for 25–30 minutes until deep golden brown. Stir in thyme if using, then set aside.

Assemble the Sandwich:
Butter one side of each bread slice. On the non-buttered side, spread Dijon mustard if using. Layer on caramelized onions and a generous handful of shredded cheeses.

Grill to Perfection:
Heat a skillet or griddle over medium heat. Place sandwiches buttered-side down and grill until golden and crisp, about 3–4 minutes per side, flipping once and pressing slightly with a spatula.

Serve Hot:
Slice in half and enjoy while the cheese is gloriously gooey and hot!

📦 Amazon Must-Haves to Help You Create the Best French Onion Grilled Cheese

• 🔪 Mandoline Slicer — Get paper-thin onion slices for perfect caramelization every time.
• 🧈 Nonstick Skillet — An even-heating, easy-to-clean skillet is essential for crisp, golden sandwiches.
• 🧀 Cheese Grater — Freshly grated cheese melts better and gives a richer flavor.
• 🍞 Bread Knife — Slice through rustic loaves cleanly without tearing or squishing.
• 🥄 French Dijon Mustard — Add a tangy touch of complexity that balances the rich cheese and onions.

💡 Helpful Tip: Don’t rush the onions—slow caramelization is key to achieving that sweet, savory depth. And for the crispiest results, press your sandwich with a spatula or use a panini press!