Preheat the oven to 350°F. Grease a 9 x 13-inch baking dish and set it aside.
Cook the pasta in salted water according to the package instructions for al dente. Reserve 2 ¼ cups of the cooking water, drain, and set the pasta aside.
1 pound rigatoni or ziti
While the pasta is cooking, make the sauce: Brown the sausage in a 6-quart saucepan, breaking it into small pieces. Once browned, add the onion, garlic, Italian seasoning, red pepper, black pepper, and salt. Cook until the onion is softened, 4-6 minutes. Then add the sage, thyme, pumpkin puree, heavy cream, and reserved pasta cooking water. Stir until combined, and bring to a simmer. Cook for 5 minutes, then remove from the heat.
1 pound sweet or spicy bulk Italian sausage, 1 medium onion, 3 cloves garlic, 2 teaspoons dried Italian seasoning, ½ teaspoon red pepper flakes, ½ teaspoon freshly ground black pepper, 1 teaspoon kosher salt, 2 tablespoons chopped fresh sage, 2 teaspoons fresh thyme leaves, 1 15-ounce can pumpkin puree, 1 cup heavy cream, 2 ¼ cups reserved pasta cooking water
Make the ricotta mixture: In a bowl, combine the ricotta, salt, black pepper, parsley, thyme, sage, Parmesan cheese, and 3 cups of mozzarella cheese. Mix together until combined.
16 ounces ricotta, ½ teaspoon kosher salt, 1 teaspoon freshly ground black pepper, ⅓ cup chopped fresh parsley, 1 teaspoon fresh thyme leaves, 2 teaspoons freshly chopped sage, ½ cup grated Parmesan cheese, 4 cups shredded mozzarella cheese
Assemble: Add the prepared pasta to the sauce and stir to combine. Pour half of the pasta into the prepared baking dish. Dollop half of the ricotta mixture over the pasta. Repeat with the remaining pasta and ricotta, then finish with the remaining mozzarella.
4 cups shredded mozzarella cheese
Bake: Cover and bake in the preheated 350°F oven for 30 minutes. Remove the cover and bake until the pasta is bubbling and the cheese is browned, 30-40 minutes. Remove and let cool for 15 minutes before serving.