Separate the ground beef into equal portions - most most likely 4 or 6 equal parts. I like to form mine into balls so they smash into a more circular burger, but it's not necessary.
Heat a large cast iron skillet over medium-high heat. You want it to be hot, so heat it for a few minutes.
Once it's hot and your burgers are ready to go, quickly brush the skillet with oil and place half of the butter on the skillet. It will smoke, so work quickly! Place one of the balls of beef on the skillet and smash it down with a spatula once or twice. You want it to be about 1/2 inch in thickness (or a little less if you wish!) and want to try and smash it only 2 or 3 times. Season it with salt and pepper and repeat with the rest of the beef. Cook them for 2 to 3 minutes and then flip, season with salt on the other side and cook for 2 minutes more. Add the cheese and let it melt.
Remove the burgers with a spatula and serve immedaitely with the house sauce, on buns, with lettuce, tomato and onion if you wish!