Pat chicken dry and season with salt and pepper. Heat oil in large skillet over medium high heat until shimmering. Add chicken, skin-side down, and brown well, then turn over and brown other side, about 10 minutes total. Remove chicken to a plate.

Pour off all but 2 tablespoons fat and add the pancetta. Cook, stirring, until lightly browned, about 3 minutes. Add the diced onions and cook until softened, scraping up any browned bits. If the bits aren't coming up or seem to be burning, pour in a little water to help deglaze the pan, a little water will do the trick. Onions should take about 2 minutes. Next, add the carrots and celery, cook until softened, another 3 minutes. Add the garlic and cook until fragrant, about 1 minute.

Add the red wine and let it reduce by one third, about 5 minutes. Stir in the tomatoes, bay leaf and rosemary, and cook briefly. Season to taste with more salt and pepper.

Nestle the chicken pieces back in the pan, spooning a little, sauce over the chicken pieces, cover and cook over medium-low heat until chicken is tender and beginning to pull away from the bone, about 35 to 40 minutes. Sprinkle with parsley before serving.