Found second pastry (5)
I believe the answer is:
start
'found' is the definition.
(as in to establish)
'second pastry' is the wordplay.
'second' becomes 's' (common abbreviation).
'pastry' becomes 'tart' (tart is a kind of pastry).
's'+'tart'='START'
(Other definitions for start that I've seen before include "Jerk" , "get under way" , "Begin to recoil?" , "Beginning" , "Commencement" .)