Cooks turning west start to simmer (5)
I believe the answer is:
'cooks' is the definition.
(stewing is a kind of cooking)
'turning west start to simmer' is the wordplay.
'turning' indicates anagramming the letters.
'start to' indicates taking the first letters.
The first letter of 'simmer' is 's'.
'west' anagrammed gives 'stew'.
(Other definitions for stews that I've seen before include "Cooks slowly in liquid" , "Simmers" , "casseroles?" , "Swelters" , "Ragouts" .)