Tart up for this fantasy? (3,2,3,3)
I believe the answer is:
pie in the sky
'this fantasy?' is the definition.
(I've seen this before)
'tart up' is the wordplay.
'tart' becomes 'pie' (I've seen this before).
'up' becomes 'inthesky'.
'pie'+'inthesky'='PIE IN THE SKY'
'for' is the link.
(Other definitions for pie in the sky that I've seen before include "Remote future benefit" , "Something that's desirable but not likely to happen" , "Something nice to think about but which is unlikely to occur" , "Inkiest hype (anag.)" , "fantasy" .)