Sharp, in a way (5)
'sharp in a way' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tart that I've seen before include "Sharp; pastry" , "sour type of pie" , "Pie with fruit filling" , "Sharp in manner, biting" , "quiche, perhaps" .)
(Other definitions for tangy that I've seen before include "characterised with relish?" , "Piquantly flavoured" , "Sharp-tasting" , "Piquant" .)