# What You Need:
→ Beef
01 - 1.1 lbs ground beef (80/20 blend recommended)
02 - 1/2 tsp salt
03 - 1/2 tsp black pepper
→ Onions
04 - 2 large yellow onions, thinly sliced
05 - 2 tbsp unsalted butter
06 - 1 tsp sugar
→ Sandwich Assembly
07 - 8 slices rye bread or sourdough
08 - 8 slices Swiss cheese or American cheese
09 - 4 tbsp unsalted butter, softened
→ Optional
10 - 1 tbsp Dijon mustard
11 - 1 tbsp mayonnaise
# Directions:
01 - Melt 2 tbsp butter in a large skillet over medium-low heat. Add sliced onions and sugar, stirring frequently until onions turn deep golden and caramelized, about 20 to 25 minutes.
02 - Season ground beef with salt and pepper. Form into 4 thin oval patties matching the size of the bread slices.
03 - In a separate skillet or grill pan over medium-high heat, sear patties for 2 to 3 minutes per side until browned and cooked through. Remove from heat.
04 - Spread a thin layer of softened butter on one side of each bread slice. Optionally spread Dijon mustard or mayonnaise on the unbuttered side. On 4 slices (unbuttered side up), layer one slice of cheese, a cooked beef patty, a generous spoonful of caramelized onions, and another slice of cheese. Top with remaining bread slices, buttered side facing out.
05 - Heat a clean skillet or griddle over medium heat. Cook assembled sandwiches 2 to 3 minutes per side, pressing gently, until bread is golden and cheese has melted.
06 - Remove sandwiches from heat, allow to rest 1 to 2 minutes, then slice in half and serve immediately.