Space behind dessert to add sugar (7)
I believe the answer is:
sweeten
'add sugar' is the definition.
(I've seen this in another clue)
'space behind dessert' is the wordplay.
'space' becomes 'en' (in printing, a space as wide as a letter 'n').
'behind' is a charade indicator (letters next to each other).
'dessert' becomes 'sweet' (synonyms).
'en' after 'sweet' is 'SWEETEN'.
'to' is the link.
(Other definitions for sweeten that I've seen before include "Make more palatable" , "pacify!" , "Add sugar etc" , "Make less bitter" , "Make sugary or saccharine" .)