Prepare the filling: in a medium skillet heat the oil over low heat. Add the onion, salt, pepper and half the sage and cook, stirring, for 5 minutes. Add the chestnuts and cook for another 4 minutes, stirring. Remove from the heat and add the panko or breadcrumbs and the apple. Add the remaining sage and taste for seasoning, adding more salt and pepper as needed.

Preheat the oven to 400 degrees.

Place the squash in a medium-sized baking or gratin dish. Season the squash with a generous amount of salt and pepper. Divide the stuffing between the two cavities, pushing down and mounding it. If you have extra stuffing you can bake it in a small skillet or baking dish alongside the squash. Dot the top of the filling with 1 tablespoon of the butter cubes and pour 1 cup of the cider on top of the stuffing and squash, letting it drip down the sides and onto the bottom of the pan.

Bake for 30 minutes. Add the remaining butter on top of the stuffing and pour the remaining ½ cup cider on top. Bake another 30 minutes, or until the squash feels tender when tested with a small, sharp knife or the tines of a fork. Serve hot or room temperature with the sage leaves as a garnish. You can serve them whole or cut in half.