Cook the Italian sausage in a large pot over medium heat, breaking it into pieces until fully browned. Use a slotted spoon to transfer the sausage to a bowl and set aside.
Add olive oil to the empty pot, then sauté the diced onion until it becomes soft and translucent, about 5 minutes. Stir in the minced garlic and cook for an additional minute until fragrant.
Pour in the chicken broth and bring the mixture to a boil. Reduce heat to low and stir in the heavy cream, oregano, basil, and red pepper flakes. Season with salt and pepper according to your taste.
Add the ditalini pasta to the simmering soup and cook until the pasta is tender but still firm, approximately 8 minutes.
Return the cooked sausage to the pot, mix in the chopped spinach, and cook for another 2 minutes or until the spinach has wilted.
Remove the pot from heat and stir in the grated Parmesan cheese until it melts and fully blends into the soup.
Ladle the soup into bowls and garnish with extra Parmesan cheese and chopped fresh parsley if desired. Serve immediately while hot.
