Patty Melts With Secret Sauce

Some of you might not know what Patty Melts is. In layman terms, it is a variation of the American cheeseburger, but this one is specially made of sourdough bread and is a melt sandwich.
This recipe usually has ground beef patty, caramelized onions, and cheese, which is a classic combination. The caramelized onions have to be slow cooked (with patience !) until soft and the glorious caramel color appears. Here, I have used the “secret” sauce which takes this sandwich to the next level. The ingredients in this sauce give a creamy, yet perfectly balanced and flavorful sauce which is a great accompaniment in this sandwich. Ensure the patties do not overcook, remove them once done and let it rest before using them in the sandwich. This keeps the sandwich juicy and full of flavor.

Ingredients:

1½ pounds ground beef
2 teaspoons Worcestershire sauce
1 teaspoon kosher salt
½ teaspoon ground black pepper
12 slices sourdough bread
½ cup Secret Sauce
3 medium Vidalia onions, thinly sliced
6 slices Cheddar cheese
8 tablespoons unsalted butter

Secret Sauce

¼ cup Dijon mustard
¼ cup mayonnaise
1 tablespoon barbecue sauce
½ teaspoon hot sauce

How to make it:

In a small bowl, stir together mustard, mayonnaise, barbecue sauce, and hot sauce. Store, covered, in refrigerator up to 3 days.
In a large bowl, combine ground beef, Worcestershire, salt, and pepper. Shape ground beef into 6 oval patties.
In a medium cast-iron skillet, melt 2 tablespoons butter over medium heat. Add onion. Cook, stirring occasionally until onion is soft and golden brown, approximately 35 minutes.
In a large cast-iron skillet, cook patties over medium-high heat until browned and cooked through, approximately 2 minutes per side.
Remove skillet from heat. Remove patties from skillet; wipe out skillet.
Layer 1 bread slice with 1 tablespoon Secret Sauce, 2 to 3 tablespoons caramelized onions, 1 slice cheese, 1 patty, and another 1 tablespoon Secret Sauce. Top with another bread slice. Repeat with remaining bread, Secret Sauce, caramelized onions, cheese, and patties.
Heat skillet over medium-high heat. Melt 2 tablespoons butter in skillet. Working in batches, cook sandwiches, flipping once, until golden brown and heated through, approximately 3 minutes per side. Add remaining butter to skillet as needed.