In a large pot or Dutch oven, heat the olive oil over medium-high heat. Add the Italian sausage and break it up with a wooden spoon as it cooks. Cook for 6-8 minutes, until browned and cooked through. Remove the sausage from the pot and set aside.

In the same pot, add the diced onion, carrot, and celery. Sauté in the sausage drippings for about 5-7 minutes, until they begin to soften. Stir occasionally. Add the minced garlic and cook for another 1-2 minutes until fragrant.

Pour in the chicken broth and diced tomatoes (with their juices). Stir well and bring to a simmer over medium-high heat. Add the Italian seasoning, salt, and black pepper. Stir again and let simmer for 10-15 minutes.

Add the uncooked ditalini pasta and stir to mix it in the broth. Reduce the heat to medium and simmer for another 10-12 minutes, or until the pasta is tender.

Once the pasta is cooked, reduce the heat to low and stir in the heavy cream. Mix until the soup is creamy. Add the grated Parmesan cheese and stir until melted and incorporated.

Return the cooked Italian sausage to the pot and stir everything together. Let the soup simmer for an additional 5 minutes. Taste and adjust seasoning if needed. Ladle into bowls and garnish with chopped parsley. Serve hot with crusty bread or a simple salad.