Screen something uplifting that'll whet the appetite (7-6)
I believe the answer is:
curtain-raiser
'that'll whet the appetite' is the definition.
The definition suggests a singular noun which matches the answer.
'screen something uplifting' is the wordplay.
'screen' becomes 'curtain' (curtain is a kind of screen).
'something uplifting' becomes 'raiser' (something that raises or lifts up).
'curtain'+'raiser'='CURTAIN-RAISER'
Can you help me to learn more?
(Other definitions for curtain-raiser that I've seen before include "Preceding event" , "Short play before the main performance" , "Preliminary event" , "drama" .)