Steps
- Toss 1 thinly sliced sweet onion with 1 tablespoon of kosher salt. Leave for 20 minutes, squeeze dry, and mix with 1 tablespoon of vegetable oil.
- Divide 285g of ground beef with 20% fat into 4 balls. Heat a 12in / 30cm cast-iron skillet over medium-high heat until very hot.
- Make 4 onion piles in the skillet. Press a beef ball firmly onto each pile with a sturdy spatula and cook over high heat for about 4 minutes, until the onions brown.
- Flip and add 4 slices of American cheese. Split 2 potato rolls and set the halves cut-side down over the patties.
- Cook for about 2 minutes, until the beef reaches 160°F / 71°C. Place 2 patties with their onions and cheese in each warmed roll.