Tart fixed with better filling (8)

I believe the answer is:

strumpet

I'm a little stuck... Click here to teach me more about this clue!

'tart' is the definition.
(I've seen this before)

'fixed with better filling' is the wordplay.
'fixed with' becomes 'set' (both can mean decided or determined. I am not sure about the 'with' bit.).
'better' becomes 'trump' (both can mean to outdo or beat).
'filling' means one lot of letters goes inside another.
'set' placed around 'trump' is 'STRUMPET'.

Can you help me to learn more?

(Other definitions for strumpet that I've seen before include "Hussy" , "Prostitute" , "... unlike her!" , "'... City' (novel by James Plunkett)" , "call girl" .)

I've seen this clue in The Times and The Sunday Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.