Flaky pastry is displaying lack of density (8)
I believe the answer is:
sparsity
'lack of density' is the definition.
'sparsity' can be an answer for 'density' (I have seen 'Low density' mean 'sparsity' so perhaps 'density' could also mean 'sparsity'). I am not certain of the 'lack of' bit.
'flaky pastry is' is the wordplay.
'flaky' indicates anagramming the letters (I've seen this in other clues).
'pastry'+'is'='pastryis'
'pastryis' anagrammed gives 'SPARSITY'.
'displaying' acts as a link.
Can you help me to learn more?
(Other definitions for sparsity that I've seen before include "Shortness of supply" , "Thinness of occurrence" , "Thinly scattered state" , "Low density" , "Thinly-scattered state" .)