Mix the beef, pork, sautéed onion, egg, milk-soaked panko, milk, Kewpie mayo, salt, pepper and nutmeg. Clap the mixture between your hands to knock out the air, then shape into patties.
Sear the patties in a hot pan, then add a splash of water, cover and steam through. Set aside.
In the same pan, simmer the ketchup, Worcestershire and soy sauce with the pan juices until glossy, then pour over the patties.
Serve with warm rice and shredded cabbage.
NOTE: Hambāgu isn't a hamburger — it's Japan's home-style meat patty, soft and juicy, always served with rice. From Shota Nakajima on Instagram.
