Biting pastry (4)
I believe the answer is:
tart
I believe this clue is a double definition.
'biting' is the first definition.
(both can mean acerbic)
'pastry' is the second definition.
(type of pastry)
(Other definitions for tart that I've seen before include "A bit sour, like flattish pie" , "Biting - pastry" , "Pie with fruit filling" , "Open-topped pie" , "Short; tangy" .)