I croon audibly – that’s sweet (5)

I believe the answer is:

icing

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

'sweet' is the definition.
(I know that icing is a type of chocolate)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for icing that I've seen before include "Cake frosting" , "Maybe Madeira's topping" , "The sweetest part of the cake" , "Sugar coating - a danger to aircraft, on roads etc" , "Sugar-coating" .)

I've seen this clue in The Mirror.

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