Moulding composite of agar and salt (8)
I believe the answer is:
astragal
'moulding composite' is the definition.
'astragal' can be an answer for 'moulding' (I've seen this before). I'm unsure of the 'composite' bit.
'of agar and salt' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'and' is a charade indicator (letters next to each other).
'agar' after 'salt' is 'saltagar'.
'saltagar' anagrammed gives 'ASTRAGAL'.
Can you help me to learn more?
(Other definitions for astragal that I've seen before include "Beaded moulding for edging furniture" , "wooden strip" .)