Bring a large pot of heavily salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Reserve 1 cup of the pasta cooking water, then drain the pasta.

While the pasta cooks, heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the Italian sausage, breaking it up with a spoon. Cook until browned and cooked through, about 5-7 minutes. Drain any excess fat.

Reduce heat to medium. Add the finely chopped yellow onion to the skillet with the sausage and cook until softened and translucent, about 4-5 minutes. Stir in the minced garlic and cook for another minute until fragrant, being careful not to burn it.

Pour in the crushed tomatoes and bring the mixture to a gentle simmer. Reduce heat to low, cover, and let it cook for 15 minutes, allowing the flavors to meld. Stir occasionally.

Uncover the sauce. Stir in the heavy cream, chopped fresh basil, and 0.5 cup of freshly grated Parmesan cheese until well combined and heated through. Season with 0.5 tsp kosher salt and 0.25 tsp freshly ground black pepper, or adjust to taste.

Add the cooked, drained pasta directly to the sauce in the skillet. Toss to coat the pasta thoroughly. If the sauce seems too thick, add a splash of the reserved pasta cooking water until it reaches your desired consistency.

Serve immediately, garnished with extra fresh basil and a generous sprinkle of additional Parmesan cheese.