Stir with black parsley perhaps (7)
I believe the answer is:
potherb
'parsley perhaps' is the definition.
(parsley is a herb)
'stir with black' is the wordplay.
'stir' becomes 'pother' (both can mean to disturb).
'with' means one lot of letters go next to another.
'black' becomes 'b' (as in pencil classifications).
'pother'+'b'='POTHERB'
(Other definitions for potherb that I've seen before include "Plant, parts of which are used in cooking" , "Flavouring plant" , "Vegetable used to flavour" , "Vegetable for flavouring" , "Plant used for seasoning in cooking" .)