- Divide the beef into 4 portions. Form each into a patty about ¾ inch thick and slightly wider than the bun. Press a shallow dimple into the center so it cooks flat.
- Keep the patties in the fridge while you butter the cut sides of the buns and toast them in a dry skillet until golden. Set aside.
- Heat a cast-iron skillet over medium-high heat until very hot. Season both sides of the patties with salt and pepper just before cooking.
- Cook without pressing for 3 to 4 minutes until a dark crust forms. Flip, lay a slice of cheese on each and cook 2 to 3 minutes more, until the center reaches 160°F (71°C).
- Rest the burgers 1 minute. Build with lettuce, tomato, onion and pickles, then add ketchup and mustard.