01 - Place a cast-iron skillet or flat griddle over high heat and allow it to get screaming hot, until the surface shimmers.
02 - Divide the ground beef into 4 equal portions and roll each into a loose ball. Do not season or pack them tightly.
03 - Spread butter on the cut sides of each bun. Place them buttered-side down in the skillet and toast until golden brown. Remove and set aside.
04 - Place the beef balls onto the hot skillet. Immediately press each one flat to about ¼-inch thickness using a sturdy metal spatula pressed over a sheet of parchment paper. Season the top side generously with salt and pepper.
05 - Cook the patties for 1½ to 2 minutes until the edges turn deeply crisp and juices bubble to the surface. Flip each patty and immediately lay a slice of cheese on top.
06 - Continue cooking for 1 more minute until the cheese is fully melted and draped over the patty.
07 - Spread burger sauce on the bottom half of each toasted bun. Layer with lettuce, a tomato slice, pickles, and sliced red onion.
08 - Place the cheesy smash patty on top of the assembled toppings, cap with the bun top, and serve immediately while hot.