8 tablespoons unsalted butter, softened and divided
2 medium Vidalia or other sweet onions, thinly sliced
2 pounds ground beef
2 teaspoons Worcestershire sauce
1 teaspoon kosher salt
½ teaspoon ground black pepper
½ cup mayonnaise
3 tablespoons Dijon mustard
2 teaspoons smoked paprika
12 slices sourdough sandwich bread
12 slices Cheddar cheese
Instructions
In a large cast-iron skillet, melt 2 tablespoons butter over medium heat. Add onion; cook, stirring occasionally, until softened and golden brown, about 35 minutes. Remove onions from skillet; wipe skillet clean.
In a large bowl, stir together beef, Worcestershire, salt, and pepper. Divide mixture into 6 portions, and shape each portion into a patty the same shape as bread.
In same skillet, cook patties over medium-high heat until browned and cooked through, 2 to 3 minutes per side. Remove patties from skillet; wipe skillet clean.
In a small bowl, stir together mayonnaise, mustard, and paprika; spread onto one side of all bread slices. Top half of bread slices with 1 slice cheese, patty, onions, 1 slice cheese, and remaining bread, spread side down.
In same skillet, melt 3 tablespoons butter over medium heat. Add 3 sandwiches; cook until bread is golden brown and cheese is melted, 3 to 4 minutes per side. Repeat with remaining 3 tablespoons butter and remaining 3 sandwiches. Serve immediately.
Recipe by Southern Cast Iron at https://southerncastiron.com/caramelized-onion-patty-melts/