Sanctimonious one inside cooked soup (5)
I believe the answer is:
pious
'sanctimonious' is the definition.
(similar in meaning)
'one inside cooked soup' is the wordplay.
'one' becomes 'i' (Roman numeral).
'inside' is an insertion indicator.
'cooked' indicates an anagram (letters cooked into a new form).
'soup' with letters rearranged gives 'pous'.
'i' going within 'pous' is 'PIOUS'.
(Other definitions for pious that I've seen before include "Devout" , "Devoutly religious" , "Dutiful" , "Good" , "Godly" .)