Caramelize the Onions: Melt 2 tbsp butter in a large skillet over medium-low heat. Add sliced onions, salt, and pepper. Cook for 20 to 25 minutes, stirring occasionally, until soft, deep golden-brown, and sweet. Transfer onions to a plate and set aside. 🧅
Form & Season Patties: Divide ground beef into 4 equal portions. Shape each portion into thin patties that closely match the shape of your bread slices. Season both sides with garlic powder, Worcestershire sauce, salt, and black pepper. 🥩
Sear the Beef Patties: Heat the skillet over medium-high heat. Add patties and cook for 3 to 4 minutes per side until well-seared and cooked through. Transfer to a plate. ⏲️
Assemble the Sandwiches: Butter one side of each slice of bread generously. On the unbuttered side of 4 slices, layer 1 slice of Swiss cheese, a cooked beef patty, a generous scoop of caramelized onions, 1 slice of Cheddar cheese, and top with another slice of bread (butter side facing out). 🥪🧀
Toast to Golden Meltiness: Wipe the skillet clean and set over medium heat. Place patty melts in the skillet (in batches if needed). Grill for 3 to 4 minutes per side, pressing down gently with a spatula, until the bread is deep golden-brown and the cheeses are completely melted! 🥪✨
Slice & Serve: Cut in half diagonally and serve piping hot alongside french fries, a side salad, or Thousand Island dipping sauce! 🍟🍽️✨
