Confectioner's first to discover truth about sweet (7)
I believe the answer is:
crumble
'truth about sweet' is the definition.
I can't judge whether this defines the answer.
'confectioner's first to discover' is the wordplay.
'confectioner's first' becomes 'c' (1st letter of 'confectioner').
'to discover' becomes 'rumble' (to rumble someone is to discover their secret).
'c'+'rumble'='CRUMBLE'
Can you help me to learn more?
(Other definitions for crumble that I've seen before include "(To) fragment; pudding" , "Break down, fall apart" , "Fall to pieces - dessert" , "Type of pudding - disintegrate" , "Gradually disintegrate" .)