Someone cocky adds more to pastry (7)
I believe the answer is:
upstart
'someone cocky adds more' is the definition.
I can't tell whether this defines the answer.
'to pastry' is the wordplay.
'to' becomes 'ups' (I am not sure about this - if you are sure you should believe this answer much more).
'pastry' becomes 'tart' (type of pastry).
'ups'+'tart'='UPSTART'
Can you help me to learn more?
(Other definitions for upstart that I've seen before include "Unexpectedly fresh" , "Tap rust (anag.)" , "One who has risen suddenly to high position, and is arrogant with it" , "Presumptuous and arrogant type" , "Person who behaves arrogantly in the new position" .)