Sample of brownie certified by family member (5)
I believe the answer is:
niece
'family member' is the definition.
(I've seen this before)
'sample of brownie certified by' is the wordplay.
'sample of' indicates a hidden word (I've seen this in other clues).
'NIECE' can be found hidden inside 'brownie certified by'.
(Other definitions for niece that I've seen before include "[PRIEST'S] daughter?" , "Female relation" , "Kinswoman" , "A younger female relative" , "Brother's girl" .)