Brown the sausage. In a large pot over medium-high heat, cook the ground Italian sausage until browned and fully cooked. Remove the sausage from the pot, leaving the rendered drippings behind.
Cook the vegetables. Add the diced onion, minced garlic, and drained tomatoes to the same pot. Cook until the onions are softened and translucent, scraping up the browned bits left behind by the sausage.
Make the roux. Add the butter and allow it to melt, then stir in the flour. Cook for approximately 1 minute, stirring to combine the flour with the butter, sausage drippings, and vegetables.
Add the broth and sausage. Return the cooked sausage to the pot. Gradually stir in the chicken broth and 1 cup of water until combined.
Cook the macaroni. Bring the soup to a simmer and add the dry elbow macaroni. Simmer for approximately 11–13 minutes, stirring occasionally, until the pasta is tender.
Finish the soup. Reduce the heat to low. Stir in the heavy cream and finely chopped Parmesan cheese until incorporated and the soup is creamy. Taste and season with salt and black pepper as needed.
Serve. Remove from the heat and allow the soup to cool slightly before serving.