Heat oven to 400° F. Rinse the chicken and pat dry with paper towels. Season with the salt and pepper.Heat the oil in a Dutch oven or large saucepan over medium heat. Add the pancetta or bacon and fry until crisp. Transfer to a plate. Spoon off and discard all but 1 tablespoon of the drippings. Add some of the chicken to the pot, skin-side down, and brown on both sides. Transfer to a plate. Repeat with the remaining chicken.Add the onions and mushrooms to the pot and cook, stirring occasionally, until the mushrooms release their juices, about 5 minutes. Add the endives and wine, increase heat to medium-high, and bring to a boil. Nestle the chicken among the endives. Cover, reduce heat, and simmer for 40 minutes. Divide the chicken, endives, and sauce among individual plates and sprinkle with the reserved pancetta or bacon.