Bring a large pot of salted water to a rolling boil and cook the rigatoni until it reaches an al dente texture, following the package instructions. Drain and set aside.

Meanwhile, in a large skillet over medium-high heat, break apart the Italian sausage and cook it with the chopped onion, stirring occasionally. Allow the meat to brown and release its flavors, which should take about 8 to 10 minutes.

Add the minced garlic to the skillet and stir, letting it cook for about 1 minute until fragrant. If there is excess fat in the pan, carefully spoon some out, but leave enough to keep the dish rich and flavorful.

Pour in the crushed tomatoes and the diced tomatoes along with their juices. Stir to combine, then lower the heat slightly and let the sauce gently simmer for about 10 minutes, allowing the flavors to meld together. If the sauce begins bubbling too aggressively, reduce the heat further.

Mix in the heavy cream and torn basil leaves (if using), then season with salt and freshly ground black pepper to taste. Let the sauce cook for another minute or two, ensuring everything is well incorporated.

Toss the drained rigatoni into the sauce, stirring well so the pasta is thoroughly coated in the creamy, tomato-rich mixture. Serve immediately, garnished with freshly grated Parmesan cheese, if desired.