Use a medium size pan and turn the heat to medium. Add oil ( I use vegetable oil ) for cooking and add the onion.
When the onion turns clear and softer, then add ground beef.
Cook until the ground beef is cooked well. Add salt, black pepper, and sugar. Stir.
Turn the heat off. If there is too much oil or water, please wipe with a paper towel. Let it cool down.
Peel and cut the potatoes into 1 inch square chunks.
Put in a microwave-safe bowl, and cover with cling wrap. Microwave for 5-6 minutes.
Open the cling wrap, and smash the potato right away.
Add the cooked onion and ground beef to the mashed potato bowl. Mix everything.
Flatten and divide into 4 portions with a spatula.
Shape each portion into a flat circle.
For Breading & deep-frying
Cover each Korokke with flour and dust with extra flour.
Beat an egg in a bowl and dip your floured Korokke, making sure to coat them completely.
Cover with panko after dipping the Korokke in egg.
Add deep-frying oil in a small or medium pot and heat to 335F (168C). When it gets to the right temperature, add one Korokke and cook for 50 seconds each side.*1
Move to a wire rack to remove oil.
Let's eat!
Let's serve! I personally love to add Tonkatsu sauce on top of it!
Notes
* Please do not add more than one Korokke into the pot at a time since the oil temperature will drop too quickly if you add too much at one time.