Preheat a cast iron skillet. In a large bowl mix ground chuck with the chopped onion, Worcestershire sauce, salt and pepper. Portion the meat mixture out to size of burger you prefer and pat out into patty. Once you have formed the patty, with your finger make an indention in the center of each patty-this will keep the burger from doming when frying. Fry the burgers until brown on both sides and continue to cook until meat is no longer pink on the inside