Mix in ingredients, tirelessly (4)
I believe the answer is:
stir
'mix' is the definition.
(I've seen this before)
'in ingredients tirelessly' is the wordplay.
'in' indicates the answer is hidden within the clue.
'STIR' is hidden within 'ingredients tirelessly'.
(Other definitions for stir that I've seen before include "Ladies' underwear" , "Move around in a liquid" , "Start to move" , "A slangy prison - whisk it" , "Move around - prison" .)