01 - Divide ground beef into 4 equal portions. Loosely roll each portion into a ball without packing tightly.
02 - Heat a large cast-iron skillet or griddle over high heat until very hot.
03 - Place beef balls on the hot skillet. Using a heavy spatula or burger press, firmly smash each ball until approximately ½-inch thick.
04 - Immediately season with salt and pepper. Cook without moving for 2 to 3 minutes until edges are deeply browned and crispy.
05 - Flip burgers and top each patty with a cheese slice. Cook 1 to 2 minutes more until cheese melts and burgers are cooked through.
06 - While burgers cook, melt butter in a separate skillet or on the griddle. Toast buns cut-side down until golden brown.
07 - Spread burger sauce on bottom buns. Layer lettuce, tomato, and onion. Add smash patties, optional pickles, and top buns.
08 - Serve burgers hot while cheese is melted and edges remain crispy.