Salad dressing ingredient used by British or American cook (5)
I believe the answer is:
broil
'american cook' is the definition.
(US term meaning to cook using a direct heat)
'salad dressing ingredient used by british' is the wordplay.
'salad dressing ingredient' becomes 'oil' (salad dressings often contain oil).
'used by' is a charade indicator (letters next to each other).
'british' becomes 'br' (abbreviation for British).
'oil' after 'br' is 'BROIL'.
'or' is the link.
(Other definitions for broil that I've seen before include "cook?" , "disturbance" , "stew" , "American heat" , "Be extremely hot" .)