Cook ignores an argument (9)
I believe the answer is:
reasoning
'argument' is the definition.
(I've seen this before)
'cook ignores an' is the wordplay.
'cook' is an anagram indicator.
'ignores'+'an'='ignoresan'
'ignoresan' anagrammed gives 'REASONING'.
(Other definitions for reasoning that I've seen before include "argument" , "Thinking coherently and logically" , "Debating" , "Thinking that is coherent and logical" , "Train of thought" .)