Preparation Steps

• Preheat a large cast-iron griddle or skillet over medium-high heat. Add the vegetable oil and let it heat until shimmering.
• Toss the thinly sliced onions with a pinch of salt and spread them in an even layer on the hot griddle. Let them cook undisturbed for 2–3 minutes to develop color.
• Divide the ground beef into 4 equal portions and loosely form each into a ball. Season each ball with a little salt and pepper.
• Place each beef ball on top of the cooking onions. Using a heavy spatula or a burger press, smash each ball flat into a thin patty, pressing the onions into the meat so they stick.
• Allow the patties to cook without moving until the edges are brown and crispy, about 3–4 minutes. Flip carefully and cook another 1–2 minutes until done.
• If using cheese, place a slice on each patty after flipping so it melts. Meanwhile, butter the buns and toast them on the griddle until golden.
• Assemble burgers by placing each patty with onions on a toasted bun and serve immediately.