Top pastry dish infused with last bit of Maldon salt (8)
I believe the answer is:
'top' is the definition.
(I know that acme can be written as pinnacle)
'pastry dish infused with last bit of maldon salt' is the wordplay.
'pastry dish' becomes 'pie' (I've seen this before).
'infused with' indicates putting letters inside.
'last bit of' says to take the final letters.
'salt' becomes 'nacl' (NaCl is the chemical formula for sodium chloride).
The last letter of 'maldon' is 'n'.
'pie' placed around 'nnacl' is 'PINNACLE'.
(Other definitions for pinnacle that I've seen before include "Crown" , "Apogee" , "High point of rock" , "The highest level" , "tip-top" .)