French Onion Skillet Smashed Burgers with Melted Gruyère

Classic French onion soup meets the ultimate smash burger. Sweet, jammy caramelized onions, nutty melted Gruyère, and crispy-edged beef patties piled onto a butter-toasted brioche bun with a swipe of Dijon aioli.

This is a burger that tastes like a bowl of French onion soup in handheld form—rich, savory, and deeply satisfying.

This recipe takes the beloved French onion soup and turns it into a crave-worthy skillet burger. Thin, crispy smashed beef patties are topped with slowly caramelized onions and aged Gruyère, then melted under a dome until the cheese turns molten gold.

The toasted brioche bun and Dijon aioli add a touch of richness and tang. It’s a perfect weeknight dinner or weekend indulgence that comes together in under an hour.

Ingredients

Why this recipe works

Caramelizing the onions slowly in butter and a splash of beef broth draws out their natural sweetness and creates a deep, savory jam that mimics the flavor of French onion soup.

The low-and-slow cooking breaks down the onions’ sharpness, turning them into a silky, rich topping that clings to the beef.

Smashing the beef into thin patties on a screaming-hot cast-iron skillet maximizes surface area, creating crispy, lacy edges and a juicy center. The high heat triggers the Maillard reaction, building a deep beefy crust that contrasts with the soft, sweet onions and creamy melted cheese.

Notes and substitutions

Use 80/20 ground beef for the best balance of flavor and juiciness—the fat keeps the patties moist and helps the edges crisp up.

Gruyère is the classic choice for French onion soup, but Swiss or provolone can substitute if needed. Brioche buns are soft and slightly sweet, but potato rolls work too.

Caramelizing onions takes time—about 30 minutes—but it’s mostly hands-off. A heavy cast-iron skillet is ideal for even heat and a good sear. If you don’t have a dome, a large metal bowl or a second skillet flipped upside down can trap the steam to melt the cheese.

• Gruyère cheese: Swiss cheese or provolone
• Brioche buns: Potato rolls or hamburger buns
• Dijon aioli: Mayonnaise mixed with 1 tsp Dijon mustard
• Beef broth: Chicken broth or water

Equipment

• Large cast-iron skillet
• Bowl for mixing onions
• Spatula for smashing
• Lid or dome for melting cheese
• Toaster or oven for buns