In a large skillet, heat the olive oil over medium heat. Add the Italian sausage and cook until browned, breaking it apart with a wooden spoon, about 5-7 minutes.

Add the diced onion and minced garlic to the skillet and sauté until the onion is translucent, about 3-4 minutes.

Stir in the rigatoni, chicken broth, Italian seasoning, red pepper flakes, and a pinch of salt and pepper. Bring to a boil.

Reduce heat to a simmer, cover, and cook for about 10-12 minutes, or until the pasta is al dente, stirring occasionally.

Once the pasta is cooked, stir in the heavy cream and chopped spinach. Cook for an additional 2-3 minutes until the spinach is wilted and the sauce is heated through.

Remove from heat and stir in grated parmesan cheese. Adjust seasoning with salt and pepper as needed.

Serve the creamy sausage rigatoni warm, garnished with extra parmesan cheese if desired.