Juicy and full of flavor, all these beefy patties need are your favorite fixings.
Preheat the broiler or preheat the oven to 400 degrees Fahrenheit. Cut the buns in half and place them cut side up on a rimmed baking sheet. Spread with the butter.
Heat a large skillet over high heat. Generously salt and pepper the beef patties. Space the patties in the skillet without touching, and cook, without turning or flattening, for 4 to 6 minutes (depending on thickness). Turn the burgers and cook for another 4 to 6 minutes. If desired, swirl the Worcestershire into the pan 2 minutes before the burgers are finished. (Do this if you have inferior meat or no ketchup.)
With 1 minute left to cook, place a cheese slice on each burger. Cover with a pot lid and cook until melted. Lay onion slices on top of the melting cheese. (If using sauteed onions, place under the cheese before melting.) Remove the burgers to a plate or board to rest for a few seconds before placing them on the buns.
Meanwhile, broil or toast the buns for 1 to 5 minutes, until golden on the cut side and still soft on the outside.
Spread mayonnaise on one side of each bun. Lay a burger on top. (Top with ketchup and mustard, if using.) Garnish with lettuce and top with the other half of the bun. Serve immediately with a side of sliced dill pickles.