Cook may use this, as it happens, in nutty olio (5,3)
I believe the answer is:
olive oil
'cook may use' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'as it happens in nutty olio' is the wordplay.
'as it happens' becomes 'live' (as in live television).
'in' is an insertion indicator.
'nutty' is an anagram indicator.
'olio' anagrammed gives 'ooil'.
'live' going into 'ooil' is 'OLIVE-OIL'.
'this' acts as a link.
Can you help me to learn more?
(Other definitions for olive oil that I've seen before include "Ingredient of salad dressing" , "Substance pressed from fruit" , "What may be extra virgin" , "Culinary liquid" , "Light yellow dressing pressed from Mediterranean tree fruits" .)