Cooking hot flan? Absolutely! (3,4)
I believe the answer is:
not half
'absolutely' is the definition.
(both can mean 'extremely')
'cooking hot flan?' is the wordplay.
'cooking' is an anagram indicator (cook can mean to falsify or distort).
'hot'+'flan'='hotflan'
'hotflan' anagrammed gives 'NOT HALF'.
(Other definitions for not half that I've seen before include "Too right!" , "Forty nine per cent" , "missing 50%" , "Absolutely (but less than 50%!)" , "Very much (but less than 50%)!" .)