Gelatinous substance again missing in recipe, initially (4)
I believe the answer is:
agar
'gelatinous substance' is the definition.
(I've seen this in another clue)
'again missing in recipe initially' is the wordplay.
'again missing in' becomes 'aga' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'initially' suggests taking the first letters.
The first letter of 'recipe' is 'r'.
'aga'+'r'='AGAR'
Can you help me to learn more?
(Other definitions for agar that I've seen before include "Jelly medium" , "Jelly got from seaweeds, used in foods" , "Substance derived from seaweed" , "a newspaper rejected" , "Medium for growth" .)