Cooking pasta with soy is treachery (8)
I believe the answer is:
apostasy
'is treachery' is the definition.
(apostasy is abandoning one's religion)
'cooking pasta with soy' is the wordplay.
'cooking' is an anagram indicator (cook can mean to falsify or distort).
'with' is a charade indicator (letters next to each other).
'pasta' after 'soy' is 'soypasta'.
'soypasta' is an anagram of 'APOSTASY'.
(Other definitions for apostasy that I've seen before include "defection" , "Abandonment of one's beliefs" , "Renunciation of religious or political beliefs" , "Abandonment of religious faith" , "Abandonment of religious beliefs" .)