Sweet nuts left filling hole (6,5)
I believe the answer is:
banana split
'sweet' is the definition.
(type of dessert or sweet)
'nuts left filling hole' is the wordplay.
'nuts' becomes 'bananas' (as in crazy).
'left' becomes 'l' (common abbreviation).
'filling' is an insertion indicator.
'hole' becomes 'pit' (a pit is a large hole).
'l' inserted into 'pit' is 'plit'.
'bananas'+'plit'='BANANA SPLIT'
(Other definitions for banana split that I've seen before include "sweet food" , "Ice cream dish" , "Ice-cream dish" , "Fruit and ice cream dessert" .)