Opening jar, ignoring recipe (4)
I believe the answer is:
gate
'opening' is the definition.
(a gate is an opening or entrance)
'jar ignoring recipe' is the wordplay.
'jar' becomes 'grate' (make unpleasant sound).
'ignoring' suggests deleting specific letters.
'recipe' becomes 'r' (abbreviation in medical prescriptions).
'grate' with 'r' removed is 'GATE'.
(Other definitions for gate that I've seen before include "Frame for closing an entrance" , "Movable opening" , "Means of entry" , "Entrance to a Dublin theatre" , "Narrow opening" .)