Bring a large pot of salted water to a boil. Add the rigatoni and cook according to package directions until al dente. Just before draining, reserve about one cup of the starchy pasta water.

While the pasta cooks, heat olive oil in a large skillet or Dutch oven over medium-high heat. Remove the sausage from its casings and add it to the skillet. Break it apart with a spoon and cook until browned, about 5-7 minutes.

Add the chopped onion to the skillet and cook until softened, about 3-4 minutes. Stir in the minced garlic and cook for another minute until fragrant.

Pour in the crushed tomatoes and season with salt and pepper. Bring to a simmer, then reduce the heat and stir in the heavy cream and half of the grated Parmesan cheese. Continue to stir until the cheese is melted and the sauce is smooth.

Add the drained rigatoni to the skillet with the sauce. Toss to combine, adding a splash of the reserved pasta water as needed to help the sauce cling to the noodles. Stir in the fresh basil, serve immediately, and top with the remaining Parmesan cheese.