Trick flipping enormous flans (9)
I believe the answer is:
stratagem
'trick' is the definition.
(I've seen this in another clue)
'flipping enormous flans' is the wordplay.
'flipping' says the letters should be written backwards.
'enormous' becomes 'mega ' (I've seen this before).
'flans' becomes 'tarts' (I've seen this before).
'mega'+'tarts'='megatarts'
'megatarts' backwards is 'STRATAGEM'.
(Other definitions for stratagem that I've seen before include "Ploy - start game (anag)" , "Cunning manoeuvre" , "A cunning plan or scheme" , "Artifice" , "Cunning plot" .)