Unaccompanied is better in cooking paella (1,8)
I believe the answer is:
a cappella
'unaccompanied' is the definition.
(thesaurus)
'better in cooking paella' is the wordplay.
'better' becomes 'cap' (I've seen this before).
'in' indicates putting letters inside.
'cooking' indicates anagramming the letters.
'paella' with letters rearranged gives 'apella'.
'cap' inserted within 'apella' is 'A CAPPELLA'.
'is' acts as a link.
(Other definitions for a cappella that I've seen before include "Of choral music, unaccompanied" , "type of singing" , "Sung without instruments" , "Unaccompanied singing" , "Sung without instrumental accompaniment" .)