# What You'll 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 tablespoons unsalted butter in a large skillet over medium-low heat. Add the thinly sliced onions and 1 teaspoon sugar. Cook, stirring frequently, until onions are deeply golden and caramelized, approximately 20 to 25 minutes. Remove from heat and set aside.
02 - Season the ground beef with salt and black pepper. Form into four thin oval patties, sized to match the bread slices.
03 - Heat a separate skillet or grill pan over medium-high heat. Cook patties for 2 to 3 minutes per side until browned and just cooked through. Remove from heat.
04 - Lay out eight slices of bread. Spread a thin layer of softened unsalted butter on one side of each slice. Optionally, spread Dijon mustard or mayonnaise on the opposite (unbuttered) side.
05 - On four slices of bread (unbuttered side facing up), layer one slice of cheese, a beef patty, a generous spoonful of caramelized onions, then another cheese slice. Top each with a remaining bread slice, buttered side facing outwards.
06 - Heat a clean skillet or griddle over medium heat. Cook sandwiches for 2 to 3 minutes per side, pressing gently, until bread is golden brown and cheese is melted.
07 - Remove sandwiches from the heat, let rest for 1 to 2 minutes, then slice each in half and serve warm.