Start by peeling off the membrane and cut away any arteries. You want the liver to have a smooth, butter-like texture; if the surface looks too broken then it will have a bitter taste.
Using a sharp knife cut the liver into long slices, at a slight angle, about 2cm thick.
Heat a non-stick frying pan over a high heat, then add a little oil. Season the liver with a little salt and add it to the pan, moving the pan as you do so to stop it from sticking.
Cook for about 30 seconds each side. Finish with a little butter for a nutty flavour.