- 4 tablespoons canola oil, divided
- 1 large yellow onion, thinly sliced (about 4 cups)
- 1 1/2 teaspoons Kosher salt, divided
- 1 1/4 pounds ground chuck
- 1/2 teaspoon black pepper
- 1/4 cup mayonnaise
- 1 tablespoon Dijon mustard
- 1 tablespoon barbecue sauce
- 1 tablespoon ketchup
- 3 ounces sharp yellow Cheddar cheese, shredded (about 3/4 cup)
- 8 (3/4 inch thick) sourdough bread slices
- 4 Swiss cheese slices
- 4 tablespoons butter, divided
Step 1: Heat 2 tablespoons of the oil in a medium skillet over medium heat. Add onion and 1/2 teaspoon of the salt. Cook, stirring often, until golden brown and soft, about 20 minutes. Set aside.
Step 2: Meanwhile, divide ground beef into 4 portions. Press each into a flat, 1/4 inch thick patty. Sprinkle with pepper and remaining 1 teaspoon salt.
Step 3: Heat remaining 2 tablespoons oil in a large cast iron skillet over medium-high heat. Cook 2 patties at a time, pressing gently, until browned but still pink in the center. 2 minutes per side. Transfer to a plate.
Step 4: Stir together mayonnaise, mustard, barbecue sauce, and ketchup in a small bowl until combined.
Step 5: Wipe out cast-iron skillet; reduce heat to medium. Divide Cheddar among 4 of the bread slices; top each with a patty, caramelized onions, Swiss cheese slice, mayonnaise mixture, and remaining bread. Melt 2 tablespoons of the butter in a skillet. Place 2 sandwiches in hot butter; cook (with another skillet on top of sandwiches to weigh them down) until golden brown and cheeses are melted, about 3 minutes per side. Repeat with remaining 2 tablespoons butter and 2 sandwiches.
Enjoy this classic from SouthernLiving!