1. Cut the potatoes roughly into chunks (make sure they're about the same size) and add them to a pot of cold water. Add 1/2 tbsp of salt and bring the water up to the boil, lower the heat to medium and cook until soft. (Pierce with a fork to test the doneness)
2. While the potatoes are boiling, take a frying pan and heat it on medium. Add 15g butter.
3. Once the butter is melted, add the onion and cook until softened and slightly translucent. (Don't let them brown.)
4. Add the ground beef and fry until it's cooked through.
5. Next, add a pinch of salt, pepper and nutmeg.
6. Mix well and then add 1 1/2 tbsp soy sauce, 1 tsp sugar and 2 tsp mirin.
7. Continue to fry until the liquid is absorbed.
8. Turn off the heat and set aside to cool slightly.
9. Transfer your cooked potatoes to a large heatproof bowl and mash them with 1 tbsp warm milk.
10. Once the potato is smooth, add the mince and mix until the ingredients are evenly distributed. (Be careful not to overmix.)
11. Transfer the mixture to a container and leave to cool.
12. Once it's cool to the touch, place a lid or plastic wrap over the top and chill in the refrigerator for 30 minutes.

Coating and frying

1. Preheat your oil to 170-180°C / 340-355°F.
2. Take a bowl and add 50ml cold water, 1 egg and 5 tbsp plain flour. Whisk together until smooth. This is your batter.
3. Prepare two plates, one with 3 tbsp of flour and one with 75g panko breadcrumbs.
4. Remove the filling from the fridge and divide into 4 pieces.
5. Roll each piece into a flat oval shape.
6. Coat the shaped korokke in plain flour, then the egg batter, then a generous coating of panko breadcrumbs.
7. Place the 2 korokke straight into the heated oil. (You can keep the other shaped korokke in the fridge/freezer while you wait for them to cook.)
8. Fry until crispy and golden.
9. Remove them from the oil, place them on a wire rack and then repeat step 7-8 to cook the rest.
10. Serve with a drizzle of Worcestershire sauce and enjoy!