In a large pot, bring water to a boil and add a pinch of salt. Cook the rigatoni according to package instructions until al dente. Drain and set aside.
While the pasta cooks, heat olive oil in a large skillet over medium heat. Add the diced onion and cook for about 3-4 minutes until it becomes translucent.
Add the minced garlic and cook for another minute, being careful not to burn it.
Remove the sausage from its casing and add it to the skillet. Break it apart with a wooden spoon and cook until browned and cooked through, about 5-7 minutes.
Pour in the chicken broth and bring to a simmer. Allow it to reduce slightly for about 2-3 minutes.
Stir in the heavy cream, Italian seasoning, salt, and pepper. Let the sauce simmer for another 3-4 minutes until it thickens slightly.
Add the cooked rigatoni to the skillet and toss to coat the pasta evenly with the creamy sausage sauce.
Remove from heat and stir in the grated Parmesan cheese until melted and well combined.
Serve immediately, garnished with fresh parsley.