Flavour enhancer found up in Mount Lassen (4)
I believe the answer is:
salt
'flavour enhancer' is the definition.
'salt' can be an answer for 'flavour' (salting is a kind of flavouring). I am unsure of the 'enhancer' bit.
'up in mount lassen' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'in' says the answer is hidden in the clue.
'tlas' is hidden within 'mount lassen'.
'tlas' reversed gives 'SALT'.
'found' acts as a link.
Can you help me to learn more?
(Other definitions for salt that I've seen before include "dry wit" , "Brackish" , "Mariner; sodium chloride" , "Pile up" , "Condiment - experienced sailor" .)