Preheat oven to 400°F. Line a sheet pan with parchment.
Drizzle squash with olive oil, season with salt and pepper, and roast cut-side down for 35–40 minutes, until tender and caramelized. Use this time to prep the other ingredients and heat your water or do some other things you need to do!
When the squash is done roasting, cook pasta in salted water until al dente; reserve 2 cups of pasta water.
Melt butter in a large skillet over medium heat until brown and nutty. Add garlic and cook 30 seconds.
Scoop roasted squash into the pan and mash with a whisk. Add pasta water, ½ cup at a time, until smooth.
Stir in cream and simmer until thickened. Add Parmesan, nutmeg, and white pepper. Season to taste.
Toss pasta in the sauce until glossy. Add more water if needed.
Serve hot with extra Parm! I also love to add a little chili crunch if I'm feeling funky!B