Heat half
of the butter and half of the oil in a large
frying pan.
Add the
onions and fry over a low heat for 10
minutes, but do not allow to brown. Remove
the onions and set aside.
Season
the liver on both sides with salt and pepper
to taste. Add the remaining oil and butter
to the pan.
When it
is foaming, add the liver and cook on a high
heat for 2 minutes on each side, or longer
if you do not like your liver pink in the
middle. Remove the liver and place on a
warmed serving plate.
Heat the
frying pan for a few seconds, then add the
wine and return the onions to the pan.
Boil
rapidly to reduce for 1 minute, then stir in
the parsley and pour the sauce over the
liver. Serve immediately.