In a large pot, bring salted water to a rolling boil over high heat. Add rigatoni pasta and cook according to the package instructions until al dente, approximately 10–12 minutes. Reserve 1 cup of pasta water for later. Drain and set aside.

In a large skillet, heat olive oil over medium heat. Add spicy Italian sausage, breaking it apart with a wooden spoon. Cook for about 5–7 minutes until browned, then transfer to a plate and set aside.

Using the same skillet, add diced onion and sauté for 3–4 minutes until translucent. Stir in minced garlic and cook for another minute until fragrant.

Add butternut squash cubes, dried thyme, and crushed red pepper flakes to the skillet. Season with salt and pepper. Cook for about 8–10 minutes until squash is tender.

Pour in heavy cream and bring to a gentle simmer, stirring frequently. Cook for 2–3 minutes to thicken slightly.

Return cooked sausage to the skillet, stirring well to combine. Adjust sauce thickness with reserved pasta water as needed.

Add drained rigatoni to the skillet, tossing gently with the creamy sauce. Stir in grated Parmesan cheese until melted.

Taste and adjust seasoning with additional salt and pepper as needed. Serve hot, garnished with chopped parsley.