# 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
# How to Cook:
01 - Melt 2 tablespoons butter in a large skillet over medium-low heat. Add sliced onions and sugar, cooking while stirring frequently until onions are deeply golden and caramelized, about 20 to 25 minutes.
02 - Season ground beef with salt and pepper. Shape into four thin oval patties, matching the size and shape of the bread slices.
03 - Cook patties in a separate skillet or grill pan over medium-high heat for 2 to 3 minutes per side, until browned and just cooked through. Remove from heat.
04 - Spread a thin layer of softened butter on one side of each bread slice. If desired, spread Dijon mustard or mayonnaise on the unbuttered side.
05 - On four bread slices with unbuttered side up, layer one slice of cheese, one beef patty, a generous spoonful of caramelized onions, and another slice of cheese. Top each with remaining bread, buttered side facing out.
06 - Heat a clean skillet or griddle over medium heat. Cook sandwiches 2 to 3 minutes per side while pressing gently until bread is golden and cheese melts.
07 - Remove from heat, let rest 1 to 2 minutes, slice in half, and serve warm.