In a small bowl, combine the mayonnaise, ketchup, Dijon mustard, and finely chopped gherkins. Mix thoroughly to create the signature house sauce, then set aside in the fridge.

Divide the minced beef into 4 equal portions (200 g each). Gently shape each portion into a flat patty slightly wider than your burger buns, as they will shrink slightly during cooking. Push a small indent into the center of each patty with your thumb to prevent them from puffing up.

Heat a heavy-based frying pan or cast-iron skillet over a high heat and brush lightly with vegetable oil. Generously season both sides of the beef patties with sea salt and cracked black pepper just before placing them in the hot pan.

Sear the patties for 3 to 4 minutes on the first side without moving them, creating a rich crust. Flip the patties over, immediately place a slice of cheddar cheese on top of each, and cook for another 3 minutes until the cheese is beautifully melted and the burgers are cooked through.

While the meat rests for a couple of minutes, toast the split brioche buns face-down in the pan juices or a separate toaster until lightly golden.

To assemble, spread a generous spoonful of the house sauce onto the bottom half of each toasted bun. Layer with lettuce, a slice of tomato, and red onion rings. Place the cheesy burger patty on top, add more sauce to the top bun, and close the burger.