Over in patisserie, I purchased a pasty (3)
I believe the answer is:
'a pasty' is the definition.
(I've seen this before)
'over in patisserie i purchased' is the wordplay.
'over' says the letters should be written backwards.
'in' says the answer is hidden in the clue.
'eip' is hidden within 'patisserie i purchased'.
'eip' written backwards gives 'PIE'.
(Other definitions for pie that I've seen before include "Confused, mixed type" , "Covered flan" , "In the sky, this dish is impractical" , "Very easy answer as" , "Slapstick missile" .)