Butter a large baking dish about 33 x 23 cm (13 x 9 ior at least 3 liters (12 cups).
In a large non-stick skillet or large saucepan, brown the squash, onions, celery, apples and garlic in half the oil for about 10 minutes. Salt and pepper. Transfer to a large bowl.
In the same pan, brown the pancetta and the minced meat in the rest of the oil. Add the mustard. Salt and pepper. Pour over the vegetables and add the rest of the ingredients. Mix well and distribute in the baking dish. Bake the stuffing in the oven for the last 30 minutes of cooking the turkey on the bottom rack. While the turkey is resting, increase the oven temperature to 180 ° C (350 ° F) and cook the stuffing for another 30 minutes or until the filling is firm and golden brown. Serve with roasted sage butter (see recipe).
If you are not cooking the turkey, bake the stuffing in an oven preheated to 180 ° C (350 ° F) for about 1 hour or until the filling is firm and golden brown.