Bubble tea ingredient (7)
I believe the answer is:
tapioca
'bubble tea ingredient' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tapioca that I've seen before include "Sago pudding" , "Starchy foodstuff" , "Pudding made from an extract of cassava" , "Pudding from the cassava root" , "it thickens" .)