Bakery product — or part, so it’s said (4)
I believe the answer is:
Here is my best explanation:
'bakery product' is the definition.
(I've seen this before)
'part so it's said' is the subsidiary indication.
'part' becomes 'role' ('role' can be a synonym of 'part').
'so it's said' indicates a 'sounds like' (homophone) clue.
'role' sounds like 'roll'.
'or' is the link.
(Other definitions for roll that I've seen before include "Barm cake", "wind", "Flatten; register", "Eg, bap", "Bap", "bun", "Register - for continental breakfast?", "Bakery product", "Pass" and "Bun".)