Heat olive oil in a large Dutch oven over medium-high heat. Add the Italian sausage and break it apart with a wooden spoon. Cook for 6 to 8 minutes, stirring occasionally, until fully browned with no pink remaining. Remove with a slotted spoon and set aside.

In the same pot, add the diced onion, carrot, and celery. Saute over medium heat in the sausage drippings for 5 to 7 minutes until softened and the onion is translucent. Add the minced garlic and cook for 1 to 2 minutes until fragrant. Watch closely to avoid burning the garlic.

Pour in the chicken broth and diced tomatoes with all their juices. Stir to combine and bring to a simmer over medium-high heat. Add Italian seasoning, salt, and black pepper. Simmer uncovered for 10 to 15 minutes until vegetables are fully tender and the broth is fragrant.

Stir in the uncooked ditalini pasta. Reduce heat to medium and simmer for 10 to 12 minutes, stirring every few minutes to prevent sticking. Check for doneness starting at 10 minutes since ditalini cooks quickly.

Reduce heat to low. Stir in the heavy cream slowly until smooth. Add the freshly grated Parmesan and stir steadily until fully melted into the broth. Do not allow the soup to boil after adding the cream.

Return the cooked sausage to the pot and stir to combine. Simmer on low for 5 more minutes to heat through. Taste and adjust seasoning as needed. Ladle into bowls and garnish with fresh chopped parsley. Serve hot.