Chop half the onion finely and cook over medium heat until soft. Add the pancetta and cook until it starts to crispen. Put the cooked pancetta and onion in a food processor together with the bread crumbs, cheese, parsley and egg and whizz until still coarse. Use this mixture as your stuffing for the chicken. Next, use your fingers to loosen the skin from the meat and then carefully push the stuffing mixture underneath the skin. Pull the skin back to cover the stuffing. In a pan with a little oil, cook the chicken skin side down for a couple of minutes, then turn and cook for another 2 minutes on the opposite side. Transfer the chicken, skin side up onto a baking tray and cook for a further 10 minutes in the oven at 200`c. Meanwhile, deglaze the frying pan with the wine and reduce by halve. Stir in the mascarpone cheese and sage and heat through. Finally, add in the pine nuts and serve the chicken with buttered French beans and new potatoes accompanied with the sauce.