Promises some cereal getting hot inside (5)
I believe the answer is:
oaths
'promises' is the definition.
(I've seen this in another clue)
'some cereal getting hot inside' is the wordplay.
'some cereal getting' becomes 'oats' (I can't justify this - if you can you should believe this answer much more).
'hot' becomes 'h' (abbreviation, eg on taps).
'inside' indicates putting letters inside.
'oats' going around 'h' is 'OATHS'.
Can you help me to learn more?
(Other definitions for oaths that I've seen before include "Profane expressions" , "Solemn vows" , "professions of loyalty" , "Imprecations" , "Solemn sworn promises" .)