01 -
Use a mandolin or a sharp knife to slice the onions paper-thin until almost translucent. Set aside.
02 -
Portion ground beef into 113-gram balls without overworking to retain juiciness.
03 -
Heat a cast iron skillet over high heat until very hot and sizzling.
04 -
Place each meat ball on the skillet and press down firmly and swiftly with a stiff metal spatula to create thin patties with crispy edges.
05 -
Pile the thinly sliced onions generously onto each patty on the skillet.
06 -
Cook for 2 to 3 minutes until the edges are brown and crusty, then flip burgers with onions intact. Scrape up browned bits to add flavor.
07 -
Place buns on top of the patties to steam for about one minute, softening them without sogginess.
08 -
Remove buns and place cheese slices on patties; cook for 30 seconds until melted.
09 -
Stack cheese-topped patties onto bottom buns, cap with steamed tops, and serve with mustard and pickles if desired.