1. 1. Preheat your oven to 375°F.

2. 2. Cook the pasta according to the package instructions until al dente, then drain and set aside.

3. 3. In a large sauté pan, melt the butter and sauté the walnuts and chopped fresh sage until fragrant, about 2 minutes. Remove and set aside.

4. 4. In the same pan, heat the olive oil and sauté the sliced mushrooms and chopped onion until softened, about 5-7 minutes.

5. 5. Stir in the tomato paste, minced garlic, and crushed red pepper flakes. Cook for 1-2 minutes.

6. 6. Add the fresh spinach, dried oregano, salt, pepper, and nutmeg. Cook until the spinach wilts.

7. 7. Slowly pour in the vegetable broth and pumpkin purée, simmering for 5 minutes to allow the flavors to meld.

8. 8. Combine the cooked pasta with the pumpkin tomato sauce and half of the shredded fontina cheese.

9. 9. Transfer the mixture to a large baking dish and top with the remaining fontina and Parmesan cheese.

10. 10. Bake for 20-25 minutes, or until the cheese is melted and bubbly.