In sweets, the centre can be awfully nice! (4)
I believe the answer is:
twee
'in sweets the' is the definition.
I can't judge whether this defines the answer.
'centre can be awfully nice' is the wordplay.
'centre' says to take the centre.
'can' becomes 'potty' (synonyms).
'be awfully nice' becomes 'wee' (I can't justify this - if you can you should give a lot more credence to this answer).
The centre of 'potty' is 't'.
't'+'wee'='TWEE'
Can you help me to learn more?
(Other definitions for twee that I've seen before include "Overly cute" , "Excessively quaint" , "Mawkish" , "Sentimentally sweet" , "Precious - sentimental" .)