Some confectionery spoils on counter (4,3)

I believe the answer is:

mars bar

I'm a little stuck... Click here to teach me more about this clue!

'some confectionery' is the definition.
The definition suggests a singular noun which matches the answer.

'spoils on counter' is the wordplay.
'spoils' becomes 'mars' ('mar' can be a synonym of 'spoil').
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'counter' becomes 'bar' (bar is a kind of counter).
'mars'+'bar'='MARS BAR'

Can you help me to learn more?

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app