Cut potatoes into bite-sized pieces and soak in water. Drain and microwave in a heatproof container for 5 minutes at 600W. Mash while hot and let cool.

Mince the onion finely.

Heat 1 tsp salad oil in a pan over medium heat. Add ground beef and pork mix and minced onion. Cook until the meat changes color. Add sake, sugar, and soy sauce, and stir until combined. Let cool.

Mix the mashed potatoes with the cooled meat mixture. Divide into 4 portions and shape into oval patties.

Coat each patty in flour, beaten egg, and breadcrumbs in order.