Butter a 2-quart gratin or casserole dish or an 8-inch square baking dish. Preheat the oven to 400 degrees.
In a large bowl, whisk together the cream and cider. Add the cubed squash, grated cheese, 1-teaspoon sea salt and fresh pepper. Toss well to mix. Pour the mixture into the buttered pan.
Using the same bowl, add the chopped onion, cubed apple and chopped fresh rosemary. Season with sea salt and fresh pepper and mix well. Pour over the squash.
Combine the crumbs with the minced garlic, nutmeg and melted butter. Sprinkle over the squash and apples. Bake until the squash and apples are tender and the top is golden brown, about 30 – 40 minutes.
Remove from the oven and let rest for 15 minutes before serving.