Boil the potato in salted water until tender. Drain and mash. A potato ricer is ideal for a smooth texture, but not essential.
Mix the potato with ham, cheese, garlic powder, egg yolk, pepper and butter. Refrigerate for 20 minutes to allow mixture to become firm. You can add salt if desired, but the ham and cheese are quite salty already.
Place the the egg, flour and breadcrumbs in separate bowls.
Take a tablespoon of potato mixture and using clean hands, roll into a cylinder shape, rounded at the ends. Dust in the flour, followed by the egg and finish in the breadcrumbs. Repeat. You will have about 16 – 18.
Heat enough oil in a medium saucepan or wok so that the croquettes are half submerged when added. Once oil is hot (test by dropping a small crust of bread in until it sizzles) cook the croquettes in batches, for 2 – 3 minutes, turning frequently, until golden and heated through.
*note: Panko crumbs are Japanese breadcrumbs which turn very crispy when fried, found in Asian supermarkets and the Asian section of most chain store supermarkets. Use regular breadcrumbs if you can’t find.