Heat the olive oil in a large pot (I use my dutch oven for this) over medium heat. Add pancetta and cook until browned, stirring occasionally, about 8 minutes. Remove and place pancetta into a large bowl.
Place the peeled, whole onions into the pot and cook for about 8 minutes. Then add the garlic and stir often for 3 minutes. Remove garlic and onions and place in the same bowl with the pancetta.
Season chicken with salt and pepper and place in the pot, skin down. Brown on all sides about 15-20 minutes. (Tip: Don't force the chicken into the pot if it all doesn't fit! Work in smaller batches). Remove chicken add to bowl the pancetta, onions and garlic.
Drain all the liquid from the pot and add the red wine and balsamic vinegar to the pot. Stir occasionally, scrapping off the brown pieces from the bottom. Bring to a boil then add the chicken broth, raisins, bay leaves, and all contents of the bowl (chicken, onions, pancetta and onions). Bring it to a boil then let simmer, partially covered, for about 35-40 minutes.
Taste and season with salt and pepper if needed. Remove the bay leaves before serving.