1. Combine the wine, vinegar, garlic, bay leaf, salt and a few grindings of pepper in a glass, enamel or stainless-steel bowl or baking dish. Add the liver, turning the slices about with a spoon until they are evenly coated. Marinate at room temperature for about 2 hours.
2. In a heavy 10- to 12-inch skillet, heat the olive oil over moderate heat until a light haze forms above it. Add the bacon and cook, stirring frequently, until golden brown and crisp.
3. Drain on a double thickness of paper towels. Remove the liver slices from the marinade and pat them dry with paper towels. Reserve the marinade. Heat the bacon fat remaining in the skillet until it splutters.
4. Add the liver and cook the slices about 2 minutes on each side, regulating the heat so they brown quickly and evenly without burning. Remove the liver to a heated platter.
5. Quickly pour the reserved marinade into the skillet and boil it uncovered over high heat until it has reduced to about half, meanwhile scraping in any browned bits clinging to the bottom and sides of the pan.
6. Taste for seasoning. Scatter the bacon pieces over the liver, pour the sauce over it and sprinkle with parsley. Serve at once, accompanied by Portuguese fried potatoes.
