Divide ground beef into 4 even portions. Loosely form into balls with your hands (do not overwork or smash into patties with your hands). Place in refrigerator until ready to cook.
Heat a large cast iron skillet or griddle on stovetop over medium heat.
Butter both sides of buns and place face down in skillet. Cook until browned and toasty. Set aside.
Increase heat to medium-high to high. Get it hot! Place 2-4 ground beef balls into hot skillet (all 4 if using a bigger skillet or griddle).
Using a heavy, flat spatula (or grill press), smash the burgers very flat.
Season with salt & pepper. Cook undisturbed until edges are browned, 2-3 minutes.
Flip patties. Cook 1 minute.
Add cheese. Cook until cheese melts and to desired doneness (1 minute for medium-rare).
Place burgers on buns and serve with your favorite toppings.