4 slices melting cheese such as American or mild cheddar
Toppings such as shredded iceberg lettuce, pickle chips, thinly sliced red onion, mustard, ketchup, and mayonnaise
Heat broiler. Divide beef into 4 rounds and place each between two layers of plastic wrap. Using a rolling pin, roll beef into 1/4-inch-thick patties. Butter inside of each bun. Place on a baking sheet, buttered side up, and toast under broiler.
Heat a large cast-iron skillet or griddle over high. Generously season patties on both sides with salt and pepper. Working in batches, cook burgers 1 to 2 minutes. Flip and top each with cheese; cover and cook 1 to 2 minutes more. Place burgers on buns and serve with desired toppings.