Preheat oven to 400 degrees F.
In a large saute pan, heat 4 tablespoons olive oil over medium heat. Add onions and cook slowly until onions are caramelized. Remove to a bowl and reserve pan.
Slice pancetta into thin rounds, and place on a baking sheet and cook in the oven until crisp, about 12 to 15 minutes. Remove and place on paper towels to drain.
Place vinegar, sugar and red wine into a 6-quart saucepan and bring to a boil. Add turnips with tops and cook for 5 minutes or until tender. Remove, drain, and set aside.
Turn the heat up to medium-high on the large skillet and add the other 4 tablespoons of olive oil. Dredge the liver in the seasoned flour and place in the pan, in batches. Cook until quite dark brown on one side, about 3 to 4 minutes, without moving, then remove from the pan. When both batches have been cooked, return it all to the pan, turning over onto the uncooked side, and add the white wine, balsamic vinegar, and caramelized onions; bring to a boil and then reduce heat and simmer 3 minutes.
Add parsley and stir to combine. Remove liver to 4 serving plates, pour sauce over, place 1 or 2 rounds of pancetta over, top with turnip halves, and serve.
Recipe courtesy of Mario Batali