Last of sugar in a possible sweet (8)
I believe the answer is:
adorable
'sweet' is the definition.
(I've seen this before)
'last of sugar in a possible' is the wordplay.
'last of' says to take the final letters.
'in' is an insertion indicator.
'possible' becomes 'doable' ('doable' can be similar in meaning to 'possible').
The final letter of 'sugar' is 'r'.
'a'+'doable'='adoable'
'r' placed within 'adoable' is 'ADORABLE'.
(Other definitions for adorable that I've seen before include "sweet" , "Lovely and attractive" , "Worthy of worship" , "Attractive - captivating" , "'Lovable, delightful (8)'" .)