Sweet pout, maintaining smiles on the outside (6)
I believe the answer is:
mousse
'sweet' is the definition.
(mousse is a kind of sweet)
'pout maintaining smiles on the outside' is the wordplay.
'pout' becomes 'moue' ('moue' can be a synonym of 'pout').
'maintaining' is an insertion indicator.
'on the outside' suggests removing the centre.
'smiles' with its centre removed is 'ss'.
'moue' enclosing 'ss' is 'MOUSSE'.
(Other definitions for mousse that I've seen before include "Creamy dessert; hair dressing" , "Foamy dish" , "Frothy, creamy dessert" , "Light savoury dish" , "Fluffy dessert - cosmetic for hair" .)