Italian boy penning one epic poem (5)
I believe the answer is:
iliad
'epic poem' is the definition.
(Iliad is an example)
'italian boy penning one' is the wordplay.
'italian' becomes 'i'.
'boy' becomes 'lid' (I can't explain this - if you can you should give a lot more credence to this answer).
'penning' means one lot of letters goes inside another.
'one' becomes 'a'.
'lid' placed around 'a' is 'liad'.
'i'+'liad'='ILIAD'
Can you help me to learn more?
(Other definitions for iliad that I've seen before include "City investment story" , "long story" , "story of Mediterranean heroism" , "ancient tale" , "A work by 7" .)