Fill a large pot with water, season generously with salt, and bring it to a rolling boil over high heat. Add the rigatoni pasta and cook for 10–12 minutes, stirring occasionally until it's al dente. Reserve about ½ cup of the pasta water, then drain the pasta and set it aside.

In a large skillet, heat a tablespoon of olive oil over medium heat. Add the Italian sausage and cook for 5–7 minutes until it’s browned and caramelized.

Add the diced onion and sauté for 3–4 minutes until it becomes translucent. Stir in the minced garlic, dried oregano, and red pepper flakes, cooking for 1–2 minutes until fragrant.

Pour in the heavy cream, stir to combine, and let it simmer for 2–3 minutes. Gradually stir in the Parmesan cheese until it melts. Use reserved pasta water if the sauce is too thick.

Toss the cooked rigatoni in the skillet with the creamy sauce, cooking together for 1–2 minutes to absorb flavors.

Adjust seasoning with salt and pepper. Transfer to a serving dish, garnish with parsley and additional Parmesan. Serve hot.