Open pie (4)
I believe the answer is:
flan
'open pie' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for flan that I've seen before include "Open tart with a sweet or savoury filling" , "Quiche" , "Baked dish filled with fruit or custard" , "Open pastry filled with savouries, fruit or custard" , "pudding!" .)