Definitely agree on the flash frying of the liver. I cut it into quite thin slices, coat lightly in seasoned flour and fry off very quickly in the pan I've used to caramelise the onions. Let it rest while you make the gravy, I deglaze the pan with a little red wine, thicken with some flour and add a stock (I use a stock pot) with a little redcurrant jelly. I'm also a fan of buttery mashed potatoes and I also love a crisp cabbage with it. I think if you cook the liver in liquid it makes it hard and rubbery.