Divide the cold ground beef into 8 loose balls, about 4 ounces each. Do not pack the meat tightly.
Mix the kosher salt, black pepper, and garlic powder in a small bowl for the burger seasoning.
Preheat the Blackstone griddle over medium-high to high heat until the surface is very hot, about 425°F to 450°F.
Spread butter or mayonnaise on the cut sides of the buns, then toast them on the griddle until golden. Set aside.
Place the beef balls on the hot griddle, leaving room between each one.
Cover each beef ball with parchment paper and smash firmly with a burger press or heavy spatula for about 10 seconds.
Remove the parchment and season the patties with the salt, pepper, and garlic powder mixture.
Cook for 60 to 90 seconds, until the edges are browned and crispy and the top has mostly lost its raw pink color.
Scrape firmly under each patty so the crust stays attached, then flip and immediately add American cheese. Use a melting dome to make quick work out of melting the cheese.
Cook for another 30 to 60 seconds, then stack two patties per burger.
Build the burgers on toasted buns with smash burger sauce, pickles, onion, lettuce, and any extra toppings you like.