Cook Pasta: Bring a large pot of salted water to a rolling boil. Cook the rigatoni until al dente according to package instructions (about 10 to 12 minutes). Dip a measuring cup into the pot to reserve 1 cup of starchy pasta water, then drain the pasta.

Puree Squash Sauce: In a high-powered blender or food processor, combine the roasted butternut squash cubes, broth, heavy cream, garlic, nutmeg, salt, and black pepper. Blend on high for 60 seconds until velvety smooth and creamy.

Crisp the Sage: Melt 2 tablespoons of butter in a large skillet or Dutch oven over medium heat. Add fresh sage leaves and fry for 1 to 2 minutes until crispy and fragrant. Transfer fried sage leaves to a paper towel, leaving the sage-infused brown butter in the skillet.

Simmer & Emulsify Pasta: Pour the smooth butternut squash puree into the skillet with the sage butter over medium-low heat. Stir in the cooked rigatoni and grated Parmigiano-Reggiano. Splash in 2 to 4 tablespoons of reserved pasta water, tossing continuously for 1 to 2 minutes until the golden sauce glosses over and clings tightly to every ridge of the pasta.

Garnish & Serve Hot: Divide into warm pasta bowls. Crown with crispy fried sage leaves, toasted chopped walnuts, freshly cracked black pepper, and shaved parmesan ribbons. Serve immediately!