Brainy type starts breakfast with a whole grain sandwich (8)
I believe the answer is:
cerebral
'brainy' is the definition.
(I've seen this before)
'breakfast with a whole grain sandwich' is the wordplay.
'breakfast' becomes 'cereal' (I've seen this before).
'with' means one lot of letters goes inside another.
'a whole grain sandwich' becomes 'br' (I am not sure about this - if you are sure you should believe this answer much more).
'cereal' going around 'br' is 'CEREBRAL'.
'type starts' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for cerebral that I've seen before include "Concerning the brain" , "Of the brain, intellectual" , "Highly intellectual" , "Relating to the brain" , "Intellectual, brainy" .)