Put ground meat, chopped onion, egg, 1/4 cup Panko, salt, pepper, and nutmeg in a large bowl. Knead very well until very sticky. Divide into 8 round pieces and flatten.
Coat with flour, then egg, and then Panko (bread crumbs). Let rest in the fridge for 15-30 minutes.
Heat deep frying oil to 350-375F, and fry the patties for 3-4 minutes each side.
Serve with shredded cabbage and Tonkatsu sauce.