Thinly slice the onion.
Divide the beef into 100g portions and shape into round patties.
Spread butter on the buns and toast them in a pan until golden brown.
Season the patties with salt and pepper, then cook them in a pan.
Place a slice of cheese on top of the cooked patty and let it melt.
Assemble the burger in the order of bun, patty, and bun to complete.