1) Using your hands, break the meat into small pieces and combine evenly but loosely on a parchment-lined baking sheet. Spread the meat out and season it generously with salt and pepper.
2) Preheat the oven to 240C/Gas 9. Place a roasting rack on a foil-lined baking sheet in the oven.
3) Divide the meat into 4 portions (about 140g each). Using your hands, form each portion into a ball-shape by gently tossing it from one hand to the other. (Don't over work or press too firmly on the meat.) Gently form each portion into a patty about 7cm wide and 2cm-thick.
4) Preheat a large cast-iron skillet over medium-low heat for 5 mins. Raise the heat to high and add the oil. Add the patties and cook, turning once, until well-browned, about 2 mins the first side, and 1 min the second side.
5) Using a spatula, transfer the hamburgers to the roasting rack in the oven and continue cooking to desired doneness, 5 mins for very rare (blue), 6 to 7 mins for rare, 8 to 9 mins for medium-rare, 10 to 11 mins for medium, and 13 to 15 mins for well-done. If you are using the cheese, top the hamburgers during their last couple of minutes of cooking to melt.
6) Transfer the hamburgers to a plate and let rest for a couple minutes before serving. Meanwhile, toast the baps. Assemble the hamburgers with the condiments and toppings of your choice. Serve.