In a clean skillet, heat the remaining 1/4 cup of olive oil. Dredge the liver in the seasoned flour, and add half of the slices to the skillet. Cook the liver, undisturbed, over moderately high heat until dark brown, 3 to 4 minutes. Transfer to a platter. Add the balsamic vinegar and caramelized onions to the skillet and bring to a boil, then reduce the heat and simmer for 3 minutes. Return the liver to the skillet and cook for a minute, then add the parsley. Transfer the liver and sauce to a platter, top with the pancetta and turnip halves and serve.