Dish is extravagant served in rhino's hide (7)
I believe the answer is:
risotto
'dish' is the definition.
(risotto is a kind of dish)
'is extravagant served in rhino's hide' is the wordplay.
'extravagant' becomes 'OTT' (abbreviation for 'over the top').
'served in' means one lot of letters goes inside another.
'rhino's hide' becomes 'ro' (I can't justify this - if you can you should give a lot more credence to this answer).
'is'+'ott'='isott'
'isott' going within 'ro' is 'RISOTTO'.
Can you help me to learn more?
(Other definitions for risotto that I've seen before include "food dish" , "It has roots in Italian rice-based dish" , "Rice/stock dish" , "Italian dish cooked with broth" , "Main course" .)