Pre-cook fresh crab essentially for Tommy, say (4,5)
I believe the answer is:
rock opera
'tommy say' is the definition.
(I know that Tommy is a rock opera)
'pre-cook fresh crab essentially' is the wordplay.
'fresh' is an anagram indicator (a fresh re-ordering of the letters).
'essentially' indicates the central letters.
The middle of 'crab' is 'ra'.
'pre'+'cook'='precook'
'precook' with letters rearranged gives 'rockope'.
'rockope'+'ra'='ROCK OPERA'
'for' acts as a link.
(Other definitions for rock opera that I've seen before include "Tommy, for example" , "Show" .)