Notes genuine breakfast (6)
I believe the answer is:
cereal
'breakfast' is the definition.
(I've seen this before)
'notes genuine' is the wordplay.
'notes' becomes 'ce'.
'genuine' becomes 'real' (similar in meaning).
'ce'+'real'='CEREAL'
(Other definitions for cereal that I've seen before include "'Wheat or maize, say (6)'" , "Grain used for food" , "11 food, maybe" , "Something for brekkie" , "Breakfast food made from grain" .)