Caramelize the onions

• Melt a little butter in a frying pan over medium heat.
• Add the sliced onion and cook, stirring occasionally, until soft and golden.
• Season with a pinch of salt.

Cook the patties

• Shape the ground beef into thin patties and season both sides with salt and pepper.
• Sear in the hot pan until browned on both sides and cooked through.
• Top each patty with a slice of American cheese and let it melt.

Toast the bread

• Butter one side of each bread slice.
• Toast the buttered sides in the pan until golden and crisp.

Assemble the patty melt

• Place a cheese-topped patty on a toasted slice, add the caramelized onions and a second cheese slice.
• Close with another toasted slice, buttered side out.
• Press gently and toast in the pan until the cheese is fully melted.

Serve

• Cut the patty melt in half and serve hot.