In a large pot over medium heat, add the Italian sausage. Cook until it's browned and cooked through, breaking it apart with a spoon as it cooks. Once browned, remove the sausage from the pot and set aside.

In the same pot, add the diced onion. Sauté until translucent, about 4-5 minutes. Once softened, add minced garlic and cook for another minute until fragrant.

Pour in the vegetable or chicken broth and bring to a gentle boil. Add the rinsed white beans and reserved sausage along with the dried thyme. Lower the heat and simmer for about 15 minutes.

Stir in the heavy cream and fresh spinach. Cook for a few minutes until the spinach wilts and the soup is heated through. Taste and adjust seasoning with salt and pepper as needed.

Ladle the soup into bowls, top with grated Parmesan cheese, and serve hot.