Divide the ground beef into 4 equal portions and gently form into loose balls, do not compact.

Heat a cast iron skillet over high heat until very hot. Place the beef balls in the skillet and immediately smash them down with a spatula to form patties.

Cook for about 2-3 minutes until a crust forms, then flip the patties.

Add a slice of cheese on top of each patty and cook for another 1-2 minutes until the cheese is melted.

Toast the burger buns lightly on the skillet.

Place the cooked patties on the bottom half of each bun, then top with lettuce, tomato, pickles, ketchup, and mustard.

Cover with the top half of the bun and serve immediately.