Bring a large pot of salted water to a boil. Add the rigatoni and cook according to package instructions until al dente. Drain and set aside, reserving about ½ cup of pasta water.

In a large skillet, heat the olive oil over medium heat. Add the sausage, breaking it apart with a wooden spoon. Cook until browned and cooked through, about 5-7 minutes.

Once the sausage is cooked, add the chopped onion and cook for another 3 minutes until soft. Stir in the minced garlic, cooking for an additional minute until fragrant.

Reduce the heat to low, carefully pour in the heavy cream, and stir to combine. Let the mixture simmer gently for about 2 minutes. Add in half of the Parmesan cheese, salt, and pepper to taste.

Gently fold the cooked rigatoni into the creamy sauce, adding a bit of reserved pasta water if needed to achieve desired consistency.

Sprinkle the remaining Parmesan cheese on top and garnish with fresh basil or parsley before serving.