Sweet FA turned on the rest, surprisingly (6)
I believe the answer is:
afters
'sweet' is the definition.
(both can mean dessert or pudding)
'fa turned on the rest surprisingly' is the wordplay.
'turned' shows that the letters should be reversed in order.
'on' is a charade indicator (letters next to each other).
'surprisingly' indicates an anagram.
'fa' written backwards gives 'af'.
'rest' is an anagram of 'ters'.
'af'+'ters'='AFTERS'
(Other definitions for afters that I've seen before include "Informal desserts may be faster" , "Dessert (colloq.)" , "Tiramisu, possibly" , "Pud" , "Dessert, sweet" .)