Mum’s drunk the setter’s very large cocktail (6)
I believe the answer is:
mimosa
'cocktail' is the definition.
(I've seen this before)
'mum's drunk the setter's very large' is the wordplay.
I cannot really understand how this works, but
'setter's' could be 'im' (referring to the person who set the crossword) and 'im' is present in the answer.
'large' could be 'os' (abbreviation for oversize) and 'os' is found within the answer.
'mum' could be 'ma' (both can mean mother) and 'ma' is found within the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mimosa that I've seen before include "Sensitive plant genus; so maim (anag.)" , "Tree with scented clustered flowers" , "Tropical shrub with yellow flowers" , "One growing sensitive" , "Tropical tree with yellow flowers" .)