What's paid for meal, perhaps parts a trifle well done! (7)
I believe the answer is:
attaboy
'what's' is the definition.
Both the answer and definition are interjections.
Perhaps they are linked in a way I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for attaboy that I've seen before include "word of encouragement" , "Come on!" , "What's said to encourage" , "Expression of encouragement, Tay boat (anag.)" .)