Pie Italian restaurant served up (4)
I believe the answer is:
Here is my best explanation:
'pie' is the definition.
'italian restaurant served up' is the subsidiary indication.
'italian restaurant' becomes 'trat' (I've seen this in other clues).
'served up' says the letters should be written in reverse.
'trat' reversed gives 'tart'.
(Other definitions for tart that I've seen before include "Sort of girl", "sour type of pie", "Short; tangy", "Open cake with jam etc", "Cutting, pastry", "fruit in this dish", "The pastry sounds bitter", "Biting; flan", "Pie with fruit filling" and "Sharp; pastry".)