In a large pot, bring salted water to a rolling boil over high heat. Add the rigatoni and cook until al dente, about 10-12 minutes. Just before draining, reserve a cup of the pasta water to adjust sauce consistency later. Drain the pasta and set aside while you prepare the sauce.

Heat a large skillet over medium heat and drizzle in olive oil. Add the spicy Italian sausage, breaking it up with a spatula. Cook for 5-7 minutes until browned and cooked through, stirring occasionally for even browning. Once done, remove the sausage from the skillet and set aside, leaving the flavorful drippings.

In the same skillet, add diced onion and sauté for 3-4 minutes until it turns translucent. Stir in minced garlic and cook for an additional minute until fragrant, taking care not to burn the garlic.

Next, add the cubed butternut squash, dried thyme, and crushed red pepper flakes to the skillet. Season with salt and pepper, then stir well. Cook the mixture for about 8-10 minutes, or until the squash is tender and lightly caramelized.

Reduce the heat to low and slowly pour in the heavy cream, stirring gently to combine. Allow the cream to simmer for 2-3 minutes, letting it thicken slightly.

Return the cooked sausage back into the skillet, stirring to incorporate it into the creamy sauce. If the sauce seems too thick, gradually add a bit of the reserved pasta water until you reach your desired consistency.

Add the drained rigatoni to the skillet, tossing gently to ensure each piece is coated in the creamy sauce. Sprinkle in grated Parmesan cheese, folding it into the mixture until melted and well combined.

Taste the creamy rigatoni and adjust salt and pepper as desired. Serve hot, garnished with freshly chopped parsley.