Appetiser and dessert — rest is sent back outside unfinished (7)
I believe the answer is:
starter
'appetiser' is the definition.
(I've seen this before)
'dessert rest is sent back outside unfinished' is the wordplay.
I cannot quite see how this works, but
'dessert' could be 'tart' (type of dessert) and 'tart' is located in the answer.
The remaining letters 'ser' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'and' is the link.
Can you help me to learn more?
(Other definitions for starter that I've seen before include "Beginner, or opening course of meal" , "cooking served first?" , "First course for beginner" , "First course of meal" , "Hors d'oeuvre" .)