It arises, of course, in cooking (5)
I believe the answer is:
steam
'cooking' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'it arises of course in' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'arises of course' becomes 'seam' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
't' placed inside 'seam' is 'STEAM'.
Can you help me to learn more?
(Other definitions for steam that I've seen before include "Vaporised water" , "Pre-digital" , "Driving force" , "Hot water suspended in air" , "Vaporous exhalation" .)