Lightly roll the pound of ground beef into 2 ounce meatballs.
Heat a 12-inch cast iron pan over medium-high heat with 2 tablespoons of vegetable oil.
When the oil is shimmery, salt and pepper your meatballs, then place 2 meatballs, seasoned side down on the griddle or pan.
Salt and pepper the topside of the meatballs on the griddle.
Put a small handful of onions on one of your meatballs.
Place your spatula flat on the other meatball and press down, flattening the meatball into a thin patty. A bacon press is a helpful tool to apply even weight, but you can use a can of beans too, just press down on the top of the can with the spatula between the can and the meat. Or if you feel like you have enough leverage, you can just use your own strength to flatten the meatball.
Now, smash the meatball with the onions on it. Let the patties cook for 1 minute.
Flip both patties. Then lay a slice of American cheese on the patty without the onions. Put your buns on. Let the patties cook for 30 seconds.
After 30 seconds, place your onion patty on top of the cheese patty and cook for 30 seconds more.
Pull your burger off the heat and set on a plate. Repeat with remaining meatballs – 2 per burger.