Heat Butter in a frying pan and cook finely chopped Onion, then add Beef Mince and cook until cooked through. Season with Salt and Pepper.
Meanwhile, peel Potatoes and cut into small pieces. Cook in salted water until soft. Drain very well and mash.
Combine mashed potatoes and beef mixture and add extra Salt & Pepper to taste if requires. Let it cool for a while.
Divide the mixture and make round patties. Cool the patties completely so that they become firm for easier handling. I recommend to refrigerate for 1 hour.
Coat with Flour, then dip in lightly whisked Egg(s) to coat, and finally coat with Panko Crumbs.
Heat deep frying Oil to around 180℃ and fry the patties for 2-3 minutes or until nicely browned. ‘Tonkatsu’ Sauce is recommended to serve with.
