Preheat your oven to 200°C (390°F). Cut the sugar pumpkin in half, scoop out the seeds, and place it cut side down on a baking sheet lined with parchment paper. Roast for about 45 minutes until the flesh is soft and caramelized.
While the pumpkin roasts, bring a large pot of salted water to a boil. Add the pasta and cook until just al dente, about 10 minutes. Drain and set aside.
Once the pumpkin is cool enough to handle, scoop out the flesh into a blender. Add a splash of cream, a pinch of nutmeg, and a pinch of salt. Blend until smooth and velvety, adjusting with more cream if needed.
Heat the large skillet over medium heat and melt the butter. Add the minced garlic and cook for about 1 minute until fragrant, stirring constantly to avoid burning.
Pour the pumpkin puree into the skillet with garlic. Warm gently, stirring occasionally, until the mixture is hot and slightly thickened, about 3-5 minutes.
Stir in the grated Parmesan cheese until melted and the sauce is smooth. Taste and adjust seasoning with a little salt if needed.
Add the cooked pasta to the skillet, tossing gently to coat the noodles with the sauce. If the sauce seems too thick, add a splash of reserved pasta water to loosen it up.
Sprinkle chili flakes over the pasta for a hint of heat, then drizzle with olive oil for shine and extra flavor. Toss again to combine everything evenly.
Serve immediately, garnished with additional Parmesan or chili flakes if desired. Enjoy the velvety, seasonal comfort of this pumpkin Alfredo pasta!