This is the famous classic from Venice (or rather my version).
While Soave is the traditional wine of the region, I sometimes make a version using Marsala, which is also extremely good (see end of Method).
The Delia Online Cookery School: Watch How to Prepare Garlic, just click the image to play
This recipe is from The Delia Collection: Italian. Serves 2
In the first frying pan, heat 1 tablespoon of the oil, then add the onions and, keeping the heat fairly high, toss them around to brown to a dark - almost black - colour round the edges.
Then add the garlic and toss that round the pan before pouring in the wine. Add some seasoning and bring everything up to simmering point, then turn the heat down to its lowest setting and let it just barely bubble without covering for about 45 minutes.
Meanwhile, prepare the liver by slicing it into the thinnest possible strips approximately 1½ inch (4 cm) in length. It is most important to keep them thin to cook as quickly as possible. When the 45 minutes are up, heat the remaining 1 tablespoon oil along with the butter, in the other frying pan and, then when the butter foams, add the strips of liver and sear them very briefly. Toss them around for only 1-2 minutes to brown at the edges - be swift and careful, as overcooking will dry them too much.
Season the liver with salt and freshly milled black pepper. Then remove the pan from the heat, add the onions from the other pan, mix together, and serve immediately.
To make Delia's Marsala version, replace the dry white wine with 275ml dry Marsala and 2 tablespoons of balsamic vinegar
You will also need two medium frying pans.