Cook the Italian sausage in a large pot over medium heat until browned, breaking it apart as it cooks, for about 5-7 minutes.
Add chopped onion and minced garlic; sauté them for 2-3 minutes until translucent and fragrant.
Pour in the chicken broth and bring the mixture to a simmer.
Stir in heavy cream and bring to a gentle simmer.
Stir in the grated Parmesan cheese until melted and smooth.
Add the chopped spinach, stir well, and cook for 2-3 minutes until wilted.
Season with salt, pepper, and Italian seasoning to taste.