Tart, escort and boob returning to city flat (4-1-5)
I believe the answer is:
pied-a-terre
'city flat' is the definition.
(I've seen this before)
'tart escort and boob returning' is the wordplay.
'tart' becomes 'pie' (both are baked goods).
'escort' becomes 'date' (escort can mean a date or partner).
'and' says to put letters next to each other.
'boob' becomes 'err' (both can mean to make an error).
'returning' says the letters should be written backwards.
'err' in reverse letter order is 'rre'.
'pie'+'date'+'rre'='PIED-A-TERRE'
'to' is the link.
(Other definitions for pied-a-terre that I've seen before include "Small home kept for occasional use" , "Dwelling for occasional use" , "Small secondary flat or house" , "Lodging kept for occasional use (French)" , "bijou accommodation" .)