Cook the Pasta: Bring a large pot of salted water to a boil. Cook the rigatoni according to package instructions. Drain and set aside, reserving 1/2 cup of pasta water.
Sauté Onions and Garlic: Heat olive oil in a large skillet over medium heat. Add diced onions and cook for 7-8 minutes, until softened and translucent. Add minced garlic and sauté for an additional 30 seconds, until fragrant.
Brown the Sausage: Add the Italian sausage to the skillet. Break it up into pieces and cook until browned, about 7-8 minutes.
Add Tomatoes and Herbs: Stir in the canned tomatoes (crushed or blended if using whole tomatoes), basil, oregano, red chili flakes, salt, and pepper. Bring to a boil, then reduce heat to low and simmer for 10 minutes, allowing the sauce to thicken and flavors to meld.
Make the Creamy Sauce: Stir in the heavy cream and 1 cup of Parmesan cheese. Simmer for an additional 5 minutes until the sauce is smooth and creamy.
Combine with Pasta: Add the cooked rigatoni to the sauce, tossing to coat evenly. If the sauce is too thick, add some reserved pasta water to reach your desired consistency.
Serve: Garnish with fresh basil and an extra sprinkle of Parmesan cheese before serving.