Heat large nonstick skillet (or cast iron skillet brushed with oil) over medium-high heat. Spread thin layer of butter on inside of buns and toast in skillet (butter side down) until lightly browned; set aside.
Season meat with 1 teaspoon season salt and loosely shape into 4 equal rounds (do not overwork). Add rounds to the hot skillet (leave room to smash). Smash with a heavy spatula until thin then sprinkle with additional seasoned salt and pepper. Do not reshape or round the edges. Cook 2 to 4 minutes without touching. Flip and immediately add cheese. Cook 1 to 2 more minutes until cheese is melted.
Transfer patties to toasted buns and layer with desired toppings.
If you like a well-done burger, let the patty cook for 1 minute after flipping before adding the cheese. Then add cheese and let cook until melted.
Nutritional information in an estimate only, without toppings.