Bring a large pot of salted water to a rolling boil. Add the rigatoni and cook according to package directions until al dente. Reserve about 1/2 cup of the pasta water, then drain the pasta and set it aside.

Heat a large skillet over medium heat. Crumble the Italian sausage into the pan and cook, stirring occasionally, until well browned and cooked through, about 6 to 8 minutes. Transfer the sausage to a plate and keep it warm.

In the same skillet, add the minced garlic and chopped onion. Sauté, stirring, until the onion is soft and translucent, about 4 minutes.

Add the chopped tomatoes to the skillet. Cook until they soften and release their juices, about 3 minutes.

Pour in the heavy cream and bring the sauce to a gentle simmer. Stir and let it thicken slightly for 2 to 3 minutes.

Return the cooked sausage to the skillet and stir to coat it in the cream sauce. Heat through for a minute or two.

Taste and season with salt and freshly ground black pepper. If the sauce seems too thick, add the reserved pasta water one tablespoon at a time until you reach the desired consistency.

Add the drained rigatoni to the skillet. Toss gently until the pasta is fully coated and evenly mixed with the sauce.

Serve immediately, topped with grated Parmesan and torn basil leaves.