What's milky, mixed up in drink? (4,6)
I believe the answer is:
malt whisky
'drink?' is the definition.
(malt whisky is a kind of drink)
'what's milky mixed up' is the wordplay.
'mixed up' indicates anagramming the letters.
'whats'+'milky'='whatsmilky'
'whatsmilky' with letters rearranged gives 'MALT WHISKY'.
'in' acts as a link.
(Other definitions for malt whisky that I've seen before include "nightcap" , "Distilled spirit" .)