Turns up with hat, an appealing little number? (4,7)
I believe the answer is:
show stopper
'an appealing little number?' is the definition.
(musical number)
'turns up with hat' is the wordplay.
'turns up' becomes 'shows' (I've seen this before).
'with' says to put letters next to each other.
'hat' becomes 'topper' (topper is a kind of hat).
'shows'+'topper'='SHOW-STOPPER'
(Other definitions for show stopper that I've seen before include "Performance receiving prolonged applause" , "headline act?" , "Act receiving huge applause" , "Number receiving very long applause" , "Prime number, perhaps" .)