Finely chop the onion and sauté it with the oil, until soft.

Add the meat and break it up with a wooden spoon. When the meat is cooked, add salt and pepper. Turn off the heat and let it cool.

Put the potatoes in a large pot, cover with water and bring to a boil. Cook the potatoes until soft.

Drain the potatoes and put them back on the fire, on low heat, so that any remaining moisture evaporates (be careful not to burn the potatoes).

Transfer the potatoes into a large bowl and mash them. Add salt, pepper and butter.

Before adding the meat into the mashed potatoes in the bowl, get rid of the juice from the meat. If the mixture is too soft it will be too hard to shape the korokke. Mix well.

Set aside till cool down so you can hold the mixture with your hands.

While the mixture is still warm, but not too hot, start shaping the korokke. Let them rest in the fridge for 15-30 minutes.

Dredge each korokke in flour, egg and Panko and put them back in the fridge till you are ready to fry them.

Deep fry them over medium high heat, until golden brown.

Transfer the korokke to a plate covered with paper towels to absorb any excess oil.

Serve immediately with Tonkatsu Sauce.