Preheat a large pot over medium heat. Add olive oil if needed and crumble the sausage into the pot. Cook until fully browned (about 5–7 minutes), then remove and set aside.

In the same pot, add the chopped onion and sauté until soft (3–4 minutes). Stir in the minced garlic (and optional carrots and celery) and cook for an additional 2 minutes.

Add the diced tomatoes (or tomato paste) and use a wooden spoon to scrape up any browned bits. Pour in the broth and return the sausage. Season with Italian seasoning, salt, and pepper. Bring to a boil, then reduce heat and let simmer for 15–20 minutes.

Lower the heat and gradually stir in the heavy cream. Sprinkle in the Parmesan cheese while stirring continuously to achieve a smooth, velvety texture.

If desired, add fresh spinach or kale and allow it to wilt. Adjust the soup’s consistency with extra broth or water if needed.

Give the soup a final taste, adjust seasonings as necessary, and serve hot.