Relating to good food (13)
'relating to good food' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gastronomic that I've seen before include "Relating to fine eating" , "Relating to the art of good food" , "Relating to fine food" , "epicurean" , "Relating to good eating" .)
(Other definitions for gastronomical that I've seen before include "Relating to the art of good eating" , "To do with fine eating" , "as regards eating" , "Suitable for gourmets" .)