Cut the squash in half lengthwise, scoop out the seeds, drizzle with oil and maple syrup and sprinkle with salt and pepper. Roast at 425F for 20-30 minutes, or until golden. (They won't be cooked through yet - you just want to get a bit of colour on them.)
In a small pot, heat another drizzle of oil and the butter over medium-high heat. When the foam subsides, add the onion and saute for 3-4 minutes, until soft. Scoop the softened squash out into the pot (or peel it and cut it into cubes), add the apple and the sage or curry powder and cook for another minute. Add the stock and cider and bring to a simmer; cook for 20-30 minutes, until the squash is soft.
Add the cream, season with salt and pepper and puree with a hand-held immersion blender. (Alternatively, puree it in a regular blender, or mash it in the pot with a potato masher until chunky.) Add a little water or extra stock if it seems too thick.