Cooked tart with one quality (5)
I believe the answer is:
trait
'quality' is the definition.
(thesaurus)
'cooked tart with one' is the wordplay.
'cooked' indicates an anagram.
'with' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'tart' anagrammed gives 'trat'.
'trat' going around 'i' is 'TRAIT'.
(Other definitions for trait that I've seen before include "Decorative band" , "Distinguishing characteristic of personality" , "A characteristic of straitened kind" , "Distinguishing feature" , "Habit" .)