Preheat your oven to 375ºF. Meanwhile, fill a large pot with generously salted water and bring it to a boil. Add your choice of dry pasta and cook until just 2 minutes shy of al dente. Drain and set aside.

In a large sauté pan, melt 2 tablespoons of butter over medium heat. Add the finely chopped walnuts and 1 tablespoon of fresh sage. Cook for about 5 minutes, stirring occasionally, until golden and aromatic.

Using the same pan, drizzle in 2 tablespoons of olive oil and add the sliced mushrooms and chopped onion. Sauté for about 8 minutes until soft and translucent.

Stir in ¼ cup of tomato paste, minced garlic, and ½ teaspoon of crushed red pepper flakes. Cook for 3 to 4 minutes, until the paste deepens to a rich brick red.

Gradually add 3 to 4 handfuls of spinach, stirring until wilted. Season with dried oregano, kosher salt, black pepper, and nutmeg.

Deglaze the pan by adding 3 cups of broth, scraping up flavorful bits. Stir in pumpkin purée, Parmesan, and fontina cheese until melted and smooth.

Add the cooked pasta to the pumpkin sauce, stirring gently until fully coated.

Transfer the mixture to a greased 13x9-inch baking dish, spreading it evenly. Sprinkle remaining fontina cheese and walnut-sage mixture on top.

Cover with foil and bake for 15 minutes. Remove foil and bake for an additional 10 minutes, until the cheese is melted and golden brown.