That time we went to an Okinawan restaurant in Nagoya - 芋んちゅう - "Imonchuu"
芋 Imo, which means potato, has a famous deep purple (紅芋 beni imo) variety in Okinawa that is used in all kinds of dishes. Needless to say I tried purple potato ice cream dessert, purple potato pizza, purple potato tempura and croquettes - and it was magnificent!
The waitress was half Japanese half Brazilian but also spoke fluent English, so she spoke to me as we were leaving and gave us these lovely Okinawan donuts! How nice!