Mickey for one scoffs second sweet (6)
I believe the answer is:
mousse
'sweet' is the definition.
(mousse is a kind of sweet)
'mickey for one scoffs second' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
'second' could be 's' (common abbreviation) and 's' is found within the answer.
The remaining letters 'muse' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mousse that I've seen before include "A hair dressing; a creamy sweet" , "Whipped creamy dessert" , "Fluffy pudding" , "Foamy dish" , "Creamy dish" .)