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

Toss the diced butternut squash with 2 tablespoons of olive oil, salt, and pepper. Spread on the baking sheet and roast for 25-30 minutes until golden-brown and tender.

Bring a large pot of salted water to a boil. Add 12 oz of fettuccine or penne and cook until al dente, about 8-10 minutes. Reserve 1 cup of pasta water, drain, and set aside.

In a large skillet, heat the remaining tablespoon of olive oil over medium heat. Add the chopped onion and sauté for about 5 minutes until translucent. Stir in garlic, chopped sage, and optional red pepper flakes; cook for an additional 1-2 minutes.

Add the roasted butternut squash to the skillet, followed by the vegetable broth. Mash some squash to release creaminess. Stir in heavy cream or coconut milk and Parmesan cheese.

Add the drained pasta to the skillet and toss with the sauce. Adjust with reserved pasta water if too thick, and season with salt and pepper.

Serve and garnish with toasted walnuts, extra Parmesan cheese, and fresh sage leaves.