Cook the rigatoni according to package directions until al dente. Drain and set aside.
Meanwhile, heat olive oil in a large skillet over medium heat.
Add the sausage and cook, breaking it up with a spoon, until browned and cooked through.
Stir in the onion and garlic, cooking until softened and fragrant, about 3–4 minutes.
Add red pepper flakes and white wine (if using). Simmer for 2–3 minutes to reduce slightly.
Pour in the heavy cream and bring to a gentle simmer. Let it cook for 5–6 minutes, stirring often.
Stir in Parmesan cheese until melted. Season with salt and pepper to taste.
Add the cooked rigatoni to the sauce and toss to coat evenly.
Serve hot, garnished with chopped parsley.