Preheat the oven to 450°F and line a large baking sheet with parchment paper.
Halve the butternut squash, peel, cube, and remove the seeds. Place the squash and onions on the baking sheet, drizzle with 1 tablespoon of olive oil, and season with salt and pepper.
Add the garlic bulbs to the sheet, drizzle each with olive oil, salt, and pepper, then scatter the rosemary sprigs around. Roast for 40–45 minutes, checking halfway and tossing the veggies.
Once roasted, transfer the butternut squash and onions to a blender. Squeeze the roasted garlic from its skins and add it in along with the coconut milk, veggie broth, salt, and pepper. Blend until smooth and creamy.
Meanwhile, bring a large pot of salted water to a boil. Add the pasta and cook according to package directions. Reserve ½ to 1 cup of the cooking water before draining.
In a large saucepan over low to medium heat, pour in the sauce and stir in ½ cup of grated Parmesan. Adjust seasoning with salt and pepper.
Add the drained pasta directly into the sauce, loosening with the reserved pasta water as needed. Toss gently until coated.
Serve warm, topped with extra Parmesan and freshly cracked black pepper.