Roll the beef into 2-inch diameter balls. I was able to get 5-6 patties out of 1 pound of ground beef. If making double cheeseburgers this is the perfect size. If making single patties, make them slightly larger.
Bring a skillet, flat cast iron griddle, or baking steel to high heat (on the stove or on the grill). Let it get very hot and brush it with a little oil.
Place beef balls on the hot skillet and immediately press down firmly with a flat spatula or burger press until the beef is smashed into a thin 1/4-1/2-inch thick patty. Season with salt and pepper to taste. To prevent sticking, place parchment paper between the beef/spatula.
Let sear for 2 minutes. The edges may split and won't be perfect. This is OK and actually preferred as it adds texture. Flip burgers, season with salt and pepper, and cook for 2 more minutes (burgers will be cooked medium and no longer pink). In the last 30 seconds, top each patty with cheese. Remove from the heat.
Toast the buns in the remaining burger grease to crisp the interior and warm the buns. It's a phenomenal touch and makes the burger that much better. Assemble as double or single cheeseburgers. Layer with shredded lettuce, pickles onion, ketchup, and mustard.