Preheat oven to 350 degrees F. Cut the squash in half through the equator and scrape out the seeds with a spoon. Cut a small piece off the rounded edge of both halves to give them a base to sit on. Place the squash halves, cut sides up, on a baking sheet and sprinkle with salt and pepper. Drizzle with oil and roast for 25 to 30 minutes until tender.

Cook the tortellini in salted boiling water according to package directions; drain well, reserving some of the pasta water. Set tortellini and pasta water aside.

In a separate saucepan heat the cream over medium heat. Add garlic and thyme; cook 5 to 7 minutes, until liquid is reduced and mixture coats the back of a wooden spoon. Add the 1 cup the Parmigiano-Reggiano and the nutmeg, stir over low heat to melt the cheese. Toss tortellini into cream mixture. (Use some of the pasta water to thin sauce, if necessary.) Season with salt and pepper, then divide among cooked squash bowls.

Turn the oven to 400 degrees F. Sprinkle the tops with Parmigiano-Reggiano and fresh sage leaves; bake for 10 minutes more, until the cheese is melted and golden.