French onion patty melts are what happens when a classic cheeseburger and a French onion soup decide to become the same meal. A seasoned beef patty cooked until browned and topped with melted provolone, stacked with deeply caramelized onions cooked low and slow in butter and finished with French onion soup mix, layered with mozzarella or white cheddar, and pressed between two mayo-coated slices of thick brioche or Texas toast that toast in the same cast iron skillet until golden, crispy, and completely irresistible. This is the comfort sandwich that earns a permanent place in the dinner rotation from the first time you make it.

The caramelized onions are the heart of this recipe and they deserve the full 20 to 25 minutes they need. Low heat, butter, patience, and the French onion soup mix stirred in at the end produce an onion topping that is sweet, deeply savory, and slightly jammy in a way that rushed onions never achieve. Every layer of this patty melt is doing something specific and the result is one of the best things you can build in a cast iron skillet.

Why You’ll Love This Recipe

The French onion soup mix is the shortcut that adds serious depth. Stirred into the caramelized onions with a splash of water, it concentrates the savory, slightly beefy onion flavor into the topping without any additional work.

The mayo-toasted bread is the technique detail that sets this apart from a standard grilled sandwich. Mayo on the outside of the bread produces a crispier, more evenly golden crust than butter and holds up better against the juicy filling.

Two cheeses are better than one. Provolone melted directly on the hot burger patty and mozzarella or white cheddar layered into the sandwich assembly means there is melted cheese running through every part of the sandwich.

The cast iron skillet does everything. The onions caramelize in it, the burgers cook in it, and the assembled patty melts toast in it. One pan from start to finish.

Ingredients Needed to Make French Onion Patty Melts

One cast iron skillet and simple ingredients. Here is what you need.

The Caramelized Onions

A small yellow onion thinly sliced and cooked in butter over medium-low heat for 20 to 25 minutes transforms into something deeply golden, sweet, and savory. The French onion soup mix packet stirred in at the end with a splash of water adds a concentrated, slightly beefy onion flavor that makes the topping taste like the best part of a bowl of French onion soup.

The Burgers

Omaha Steaks burgers are an excellent choice for their consistent quality and thickness. Any good ground beef patty at 80/20 fat content works equally well. Creole Trinity and Herb seasoning, salt, and pepper season the patties before cooking. Provolone melted directly on the hot patty is the first cheese layer.

The Build

Thick brioche buns or Texas toast are both excellent choices with enough structure to hold the weight of the filling without becoming soggy. Mayonnaise spread on the outside of the bread is the toasting fat that produces the golden, crispy exterior crust.

How to Make French Onion Patty Melts

1

Heat the cast iron skillet over medium-low heat. Add the butter and the thinly sliced onions. Cook for 20 to 25 minutes, stirring every few minutes, until the onions are deeply golden, soft, and sweet-smelling throughout. Do not rush this step by increasing the heat. High heat produces softened onions with a pale, slightly bitter result rather than the deep, jammy caramelization that makes these patty melts extraordinary. Once the onions are deeply caramelized, stir in the French onion soup mix and a splash of water. Cook for another minute until everything is combined and cohesive. Remove from the skillet and set aside.

2

Increase the heat to medium-high. Season the burger patties on both sides with CTH seasoning, salt, and pepper. Add to the hot skillet and cook to your preferred doneness, about 3 to 4 minutes per side for medium. In the last minute of cooking, place a slice of provolone on each patty and cover the skillet briefly to melt the cheese completely. Remove the patties and set aside.

3

Spread a thin, even layer of mayo on the outside of each bread slice. The mayo side goes against the hot skillet surface when toasting. On the inside of the bottom bread slice, place the cheesy burger patty. Top with a generous spoonful of the caramelized onions. Add a slice of mozzarella or white cheddar over the onions. Press the top bread slice on, mayo side facing out.

4

Reduce the heat to medium. Place the assembled patty melts in the skillet and cook for 2 to 3 minutes per side, pressing down gently with a spatula for even contact between the bread and the skillet surface. Toast until both sides are deeply golden and crispy and the internal cheese layer is fully melted. Slice in half and serve immediately.