Bring a large pot of salted water to a boil and cook the rigatoni according to package instructions until al dente. Drain and set aside.
In a large skillet over medium heat, heat the olive oil. Add the Italian sausage, breaking it apart with a wooden spoon. Cook until browned, about 5-7 minutes.
Once the sausage is cooked through, add the chopped onion and cook for an additional 3-4 minutes until the onion is translucent.
Stir in the minced garlic and cook for another minute until fragrant.
Pour in the chicken broth, and scrape the bottom of the skillet to release any browned bits. Allow it to simmer for about 3 minutes.
Reduce heat to low, then add the heavy cream, Italian seasoning, red pepper flakes, and Parmesan cheese. Stir until the cheese has melted and the sauce is well combined.
Add the fresh spinach to the sauce, and stir until wilted, about 2 minutes. Season with salt and pepper to taste.
Finally, gently fold in the cooked rigatoni and toss until the pasta is well coated with the creamy sauce.
Remove from heat and let it sit for a couple of minutes to thicken slightly before serving.
Notes
Serve in deep bowls, garnished with fresh basil leaves and an extra sprinkle of grated Parmesan on top for an appealing finish.