An advertisement for pastry? (4)
I believe the answer is:
puff
This clue is a double definition.
'an advertisement' is the first definition.
(I've seen this before)
'for pastry?' is the second definition.
(puff is a kind of pastry)
(Other definitions for puff that I've seen before include "Short burst of air" , "Smoke - light pastry" , "Quick emission of smoke etc" , "Advertisement; smoke a cigarette" , "type of pastry" .)