Cook's ultimate advantage concerning English rice dish (8)
I believe the answer is:
kedgeree
'rice dish' is the definition.
(I've seen this before)
'cook's ultimate advantage concerning english' is the wordplay.
'ultimate' indicates one should take the final letters.
'advantage' becomes 'edge' (edge is a kind of advantage).
'concerning' becomes 're'.
'english' becomes 'e' (abbreviation).
The last letter of 'cook' is 'k'.
'k'+'edge'+'re'+'e'='KEDGEREE'
(Other definitions for kedgeree that I've seen before include "Dish of rice, hard-boiled eggs and cooked flaked fish" , "Rice dish with boiled eggs and flaked fish" , "Food" , "Indian rice dish" , "Fishy breakfast dish" .)