Prepare the Beef: If you haven't bought pre-sliced beef, take your slightly frozen sirloin steak and, using a very sharp knife, slice it as thinly as possible (about 2-3mm thick) against the grain. Place the sliced beef in a large bowl.

Make the Marinade: In a separate medium bowl, combine the soy sauce, toasted sesame oil, brown sugar, grated Asian pear, minced garlic, grated ginger, black pepper, and mirin (if using). Whisk everything together until the sugar has completely dissolved.

Marinate the Beef: Pour the marinade over the sliced beef. Use your hands or a spoon to gently massage the marinade into the meat, ensuring every piece is well-coated. What works best for me is to really get in there with my hands to make sure it's all covered.

Let it Rest: Cover the bowl with cling film and place it in the refrigerator to marinate for at least 2 hours. For the best, most developed flavour, you can leave it to marinate for up to 24 hours.

Prepare for Cooking: Before you're ready to cook, remove the beef from the fridge and let it sit at room temperature for about 20 minutes. This helps it cook more evenly.

Cook the Beef: Heat the neutral oil in a large cast-iron skillet or frying pan over medium-high heat. The pan needs to be properly hot. Working in batches to avoid overcrowding the pan, add a single layer of beef. Cook for 1-2 minutes per side, until it's browned and has developed caramelised, slightly charred edges.

Serve Immediately: Remove the cooked beef from the pan and place it on a serving platter. Repeat with the remaining beef. Garnish generously with the sliced spring onions and toasted sesame seeds, and serve straight away.