Preheat a cast iron skillet over medium-high heat until very hot.

Divide the ground beef into 4 equal portions and roll into balls.

Place the beef balls in the skillet and immediately smash them down with a spatula to form patties.

Cook for about 3-4 minutes until a crust forms, then flip the patties.

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

Toast the burger buns in the skillet until golden brown.

Spread ketchup and mustard on the bottom bun.

Add the lettuce, followed by the burger patty with melted cheese.

Top with sliced tomatoes and pickles, then place the top bun on.