Begin a small cake (5)
I believe the answer is:
start
'begin' is the definition.
(I know that start is a kind of begin)
'a small cake' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for start that I've seen before include "Begin; flinch" , "Onset" , "Jerk" , "get under way" , "Begin - opening move" .)