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

Toss diced butternut squash with 1 tablespoon of olive oil, salt, and pepper on the baking sheet.

Roast for 25-30 minutes, stirring halfway through, until golden brown and fork-tender.

Boil a large pot of salted water, add pasta, and cook according to package instructions until al dente. Reserve 1 cup of pasta water before draining.

In a skillet, heat the remaining 2 tablespoons of olive oil over medium heat and sauté the onion for about 5 minutes until translucent.

Add minced garlic, chopped sage, and red pepper flakes, cooking for another 1-2 minutes.

Add roasted butternut squash, mash some pieces, and incorporate vegetable broth, heavy cream, and Parmesan cheese.

Adjust sauce thickness with reserved pasta water and season to taste.

Toss in the drained pasta until evenly coated with sauce, and serve topped with toasted walnuts, extra Parmesan, and fresh sage leaves.