Cook pasta according to package directions. Reserve ½ cup pasta water, then drain the pasta and set aside.
While the pasta cooks, make the sauce: Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the sausage, break it up with a wooden spoon, and cook for about 5 minutes, stirring occasionally, until it’s just cooked through. Remove the sausage from the pan.
In the same skillet, heat the remaining 1 tablespoon olive oil over medium heat. Add the shallots and garlic and cook for 2 minutes, stirring often, until the shallots begin to soften.
Add the tomato paste and cook, stirring, for 1 minute. Stir in the canned pumpkin, heavy cream, salt, pepper, nutmeg, chili flakes, and parmesan cheese. Let simmer for 2 minutes, then turn off the heat.
To a small skillet over medium-low, add the butter. Cook, whisking often, for about 6-7 minutes until the butter has turned golden brown. Add the chopped walnuts and sage and cook for 5 minutes until toasted. Turn off the heat.
Add the cooked pasta, cooked sausage, and ¼ cup pasta water to the pumpkin sauce and stir until well-coated. If needed, add more pasta water until the sauce is creamy and glossy. Taste and add more salt and pepper if desired.
Serve pasta in shallow bowls with the crispy walnut sage topping, more parmesan cheese, and a sprinkle of parsley on top. Enjoy!
