# Ingredient list:
→ Patties
01 - 1 lb ground beef (80/20 blend)
02 - 1 tsp Worcestershire sauce
03 - 1/2 tsp garlic powder
04 - 1/2 tsp kosher salt
05 - 1/4 tsp freshly ground black pepper
→ Onions
06 - 2 large yellow onions, thinly sliced
07 - 2 tbsp unsalted butter
08 - 1/4 tsp salt
→ Assembly
09 - 8 slices rye bread
10 - 8 slices Swiss cheese
11 - 4 tbsp unsalted butter, softened
12 - Optional: 2 tbsp mayonnaise
# Cooking steps:
01 - In a bowl, mix ground beef with Worcestershire sauce, garlic powder, kosher salt, and black pepper. Shape into 4 equal patties, slightly larger than bread slices.
02 - Heat cast iron skillet over medium heat. Add 2 tablespoons butter, sliced onions, and 1/4 teaspoon salt. Cook, stirring occasionally, until golden and caramelized, about 12 to 15 minutes. Remove onions from skillet and set aside.
03 - Increase heat to medium-high and add beef patties. Cook 3 to 4 minutes per side until browned and fully cooked. Remove and set aside.
04 - Wipe skillet clean. Butter one side of each bread slice. Place 4 slices buttered side down in skillet. Top each with a slice of Swiss cheese, a beef patty, caramelized onions, another slice of Swiss cheese, then cover with remaining bread slices, buttered side up.
05 - Cook over medium heat until bread is golden brown and cheese melts, about 3 minutes per side. Press gently with spatula to develop even crust.
06 - Slice each sandwich in half and serve immediately while hot.
