In a large pot, bring salted water to a boil. Add 1 pound uncooked pasta and cook to al dente, according to package instructions. Drain the water and set aside. Note: you may reserve 1 cup of pasta water if you want. I used vegetable stock instead of pasta water.
In a skillet, add 1 tablespoon butter and minced 2 garlic cloves. Cook for 1 minute on low-medium heat until garlic is fragrant.
Add 1 cup panko breadcrumbs and ¼ teaspoon Italian seasoning and cook, stirring in between until golden brown and toasted. Take the skillet off the heat and set aside.
In a large pot or skillet, add 2 tablespoons butter, minced 4 garlic cloves, and chopped ½ large yellow onion and cook for 2 minutes or until sautéed onion turns soft.
Add 2 cups pumpkin purée and stir. Add ¾-1 teaspoon salt, ½ teaspoon fresh ground black pepper, ¼ teaspoon red pepper flakes, 3-4 fresh thyme leaves, and chopped 2 fresh rosemary leaves and cook for 1 minute, stirring continuously.
Pour the 1 cup vegetable stock and stir until combined. Stir in the 1 cup heavy cream and let the sauce simmer for 1-2 minutes.
Add the cooked pasta and toss to coat. If you feel the sauce is too thick for your liking, you may add more vegetable stock or pasta water. Fold in the grated ½ cup parmesan cheese and 6 ounces baby spinach, and cook for another 30 seconds to 1 minute. The spinach will wilt in the heat.
Top with toasted breadcrumbs and serve warm.