We hear donkey calls for cook slowly (6)
I believe the answer is:
braise
'cook slowly' is the definition.
(I've seen this in another clue)
'we hear donkey calls' is the wordplay.
'we hear' shows a homophone (sound like).
'donkey calls' becomes 'brays' (donkeys bray).
'brays' is a homophone of 'BRAISE'.
'for' is the link.
(Other definitions for braise that I've seen before include "Stew in a closed pan" , "Fry then stew (meat)" , "Heat slowly" , "Cook slowly with little water in closed container" , "Rabies (anag.)" .)