A flan’s turned over, revealing layers (6)
I believe the answer is:
strata
'layers' is the definition.
(I know this)
'a flan's turned over' is the wordplay.
'flan's' becomes 'tart's'.
'turned over' is a reversal indicator.
'a'+'tarts'='atarts'
'atarts' reversed gives 'STRATA'.
'revealing' is the link.
(Other definitions for strata that I've seen before include "Beds of sedimentary rock" , "Layers as of rock in the earth's crust" , "Layers of sedimentary rock" , "Geological layers" , "hard beds" .)