What Oasis made, having drained beer, vermouth and soft drink (7)
I believe the answer is:
britpop
'what oasis made' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'drained beer vermouth and soft drink' is the wordplay.
'drained' says to hollow out the word (remove centre letters).
'vermouth' becomes 'it' (short for 'Italian vermouth' as in 'gin and it').
'and' says to put letters next to each other.
'soft drink' becomes 'pop' (pop is a kind of soft drink).
'beer' with its middle taken out is 'br'.
'br'+'it'+'pop'='BRITPOP'
'having' is the link.
Can you help me to learn more?
(Other definitions for britpop that I've seen before include "1990s popular music style" , "Blur, Oasis et al" , "1990s' style of UK music" , "1990s musical movement" , "music genre" .)