The liver has to be eaten hot, as soon as it is prepared. It can't be enjoyed afterward, because it hardens when heated.
- Slice the onions and sauté them in a pan with butter and oil. When they start to get brown, add a little vinegar (if you decide to use it) or two spoons of water. Cook over low heat for 15/20 minutes.
- Cut the liver into small slices and add it to the onions. If you like, add parsley. Cook fast (no more than 5 minutes) over high heat. Season with salt and pepper.
- Liver is best served with soft polenta or with baked polenta slices.
Some additional ingredients: butter and a good extra virgin olive oil to brown the onions, vinegar (optional), parsley. Some add white wine or lemon instead of vinegar. These alternatives might outrage the purists, nonetheless they derive from family traditions, which makes them worthy of respect.
Liver belongs to Italian culinary tradition and is the most eaten of the offal. You can find evidences of the use of liver already in the Roman era, as confirmed by Apicius’ work De re coquinaria. In Latin, liver was called “iecur”. Apicius, in order to obtain a very fat liver, used to feed the animals (mainly cows and gooses) with figs (“ficus” in Latin): hence the name iecur ficatum (liver with figs), then abbreviated as ficatum and adapted as “fegato” (liver).
Instead of figs, the wise Venetian chefs used sio’le (onions), as they were very common in the lagoon and could smoothen the taste of liver the same way as figs. Apparently, the Venetian recipe was so appreciated that it was also mentioned in the Apicio moderno (Modern Apicius) written in 1790 by Francesco Leonardi, under the name “Fegato di mongana alla veneziana” (mongana is the milk-fed veal).