1. Prepare the butternut squash: Preheat your oven to 400 F (200 C). Carefully cut the butternut squash in half lengthwise. Use a spoon to scoop out the seeds and stringy bits. Lightly brush the cut sides with olive oil and sprinkle with a pinch of salt and pepper. Place the squash halves cut-side down on a baking sheet.

2. Roast the squash: Bake the squash in the preheated oven for 30-40 minutes, or until it is tender when pierced with a fork. The skin should be slightly browned, and the flesh should be soft. While the squash is roasting, you can prepare the stuffing.

3. Cook the sausage: In a large skillet over medium-high heat, crumble and cook the bulk pork sausage until it is fully browned and no longer pink. Break up any large pieces with a spoon as it cooks. Drain off any excess grease from the skillet.

4. Saute the apple and sourdough: Add the diced apple and torn sourdough bread pieces to the skillet with the cooked sausage. Cook for about 5-7 minutes, stirring occasionally, until the apples start to soften and the sourdough begins to toast slightly.

5. Combine the stuffing ingredients: Stir in the fresh chopped sage and chicken broth into the sausage and apple mixture. Cook for another 2-3 minutes, allowing the broth to be absorbed and the flavors to meld. Taste the stuffing and adjust seasoning with salt and pepper as needed.

6. Stuff and finish baking: Once the roasted butternut squash is tender, remove it from the oven. Carefully flip the halves over. Fill each squash half generously with the prepared sausage and apple stuffing. If using, sprinkle the shredded Parmesan cheese over the top of the stuffing.

7. Final bake: Return the stuffed squash to the oven and bake for an additional 10-15 minutes, or until the stuffing is heated through and the cheese (if used) is melted and lightly golden. Serve hot.