The drink that flummoxed teenager (5,3)
I believe the answer is:
green tea
'the drink' is the definition.
(type of tea)
'flummoxed teenager' is the wordplay.
'teenager' can be anagrammed to 'GREEN TEA'.
Though, I'm not sure how the anagram is indicated.
'that' is the link.
Can you help me to learn more?
(Other definitions for green tea that I've seen before include "Healthy drink" , "brew-up?" , "Brewed" , "'Asian herbal drink (5,3)'" , "Oriental leaves" .)