Add potatoes to a large pot of salt water, and bring them to a boil, cook until tender, about 15 minite. Drain. Pour potatoes into a large bowl. Stir in butter, and mash with fork or potatoe masher. Set aside

Heat 1 tablespoon oil in a large skillet over medium heat. Stir in onions and cook until soft. Stiff in beef and soy sauce. Cook, stirring continuously until beef is browned and all the liquid is evaporated. Combine beef and onion with potatoes, stir well.

Heat 1/2 cup oil in a deep skillet or wok over medium-high heat.

Shape potatoe and beef mixture into 10 similar sized patties. Dredge parties in flour l. Then dip in egg, and coat with panko bread crumbs. Carefully place patties into oil, and fry until golden brown on each side.