1. Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.

2. Carefully slice the spaghetti squash in half lengthwise and scoop out the seeds.

3. Drizzle the cut sides of the squash with olive oil, then season with half of the salt and half of the black pepper.

4. Place the squash halves cut side down on the prepared baking sheet and roast for 35–40 minutes, or until the flesh is tender when pierced with a fork.

5. Remove the squash from the oven and let it cool just enough to handle.

6. Use a fork to gently shred the squash flesh into long strands, keeping the shells intact as “boats” and leaving a thin border of squash attached to the skin.

7. Transfer most of the shredded squash strands to a large mixing bowl, reserving the shells for stuffing.

8. In a large skillet, melt the butter over medium heat.

9. Add the minced garlic and cook for 30–60 seconds until fragrant, stirring often so it doesn’t brown.

10. Pour in the heavy cream and bring it to a gentle simmer.

11. Whisk in the grated Parmesan cheese until the sauce is smooth and slightly thickened.

12. Season the Alfredo sauce with the remaining salt, remaining black pepper, ground nutmeg, and red pepper flakes if using.

13. Pour the warm Alfredo sauce over the shredded squash strands in the mixing bowl.

14. Toss gently until all of the squash is evenly coated with the sauce.

15. Fold in the chopped fresh parsley and taste, adjusting seasoning as needed.

16. Spoon the creamy squash mixture back into the two squash shells, mounding it slightly.

17. Top each stuffed squash half with the shredded mozzarella and a little extra Parmesan.

18. Return the stuffed squash halves to the oven and bake for 10–15 minutes, until heated through and the cheese is melted.

19. Switch the oven to broil and broil for 1–3 minutes, watching closely, until the top is golden and bubbly.

20. Remove from the oven, let rest for a few minutes, then garnish with extra parsley and serve warm.