Tart will have sex covered in cream (7)
I believe the answer is:
trollop
'tart' is the definition.
(synonyms)
'sex covered in cream' is the wordplay.
'sex' becomes 'roll' (having 'a roll in the hay' means having sex).
'covered in' indicates putting letters inside.
'cream' becomes 'top' (as in the cream of the crop).
'roll' put into 'top' is 'TROLLOP'.
'will have' is the link.
(Other definitions for trollop that I've seen before include "Promiscuous woman" , "Disreputable woman" , "Baggage" , "Wanton woman" , "Prostitute" .)