Opera by Verdi or Mascagni once recast to include bass (5,10)
I believe the answer is:
simon boccanegra
'opera' is the definition.
(I've seen this before)
'or mascagni once recast to include bass' is the wordplay.
'recast' indicates anagramming the letters.
'to include' means one lot of letters goes inside another.
'bass' becomes 'b' (musical abbreviation).
'or'+'mascagni'+'once'='ormascagnionce'
'ormascagnionce' is an anagram of 'simonoccanegra'.
'simonoccanegra' going around 'b' is 'SIMON BOCCANEGRA'.
'by verdi' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Another definition for simon boccanegra that I've seen is " Opera".)