2 tablespoons unsalted butter  1 tablespoon all-purpose flour 2 tablespoons olive oil   salt and freshly milled black pepper 1 medium onion, sliced very finely 1/2 pound calves' liver Juice from 1 pomegranate     In a heavy-bottomed frying pan over medium to low heat, heat 1 tablespoon each of the butter and oil. Add the onions and cook until they're soft, about 10 minutes for over half the pomegranate juice and a little water, 1-2 tablespoons,  and cook for another 10 minutes or so until the liquid's absorbed and you have a soft, sweet, and bronzy-puce tangle of onions in the pan. Remove to warmed plates and tent over with foil to stop them cooling. Add the remaining tablespoons of butter and oil to the frying pan. Mix the flour with the salt and pepper to taste and dredge the liver lightly in this mixture, and fry in the butter and oil for a minute or so on each side. Remove from the pan and put on the waiting plates with the onions. To the remaining pomegranate juice, add half its volume in water. Add this to the hot pan and deglaze. Correct the seasoning, if necessary, and pour over the liver and onions. I like this with plain boiled potatoes.  Serves 2.   Recipe courtesy of "How To Eat," by Nigella Lawson, Wiley Publishing, 2007.