1. 1. Brown the Sausage: Heat the olive oil in a large pot or Dutch oven over medium-high heat. Add the Italian sausage, breaking it up with a spoon as it cooks. Cook until the sausage is fully browned and no longer pink, about 5-7 minutes. Drain any excess grease from the pot.

2. 2. Saute Aromatics: Add the chopped yellow onion to the pot with the cooked sausage. Cook, stirring occasionally, until the onion softens and becomes translucent, about 3-5 minutes. Stir in the minced garlic and cook for another minute until fragrant, being careful not to burn it.

3. 3. Build the Broth Base: Pour in the chicken broth and add the undrained diced tomatoes. Stir in the dried Italian seasoning, salt, and black pepper. Bring the mixture to a gentle simmer, then reduce the heat to low, cover, and let it simmer for 10 minutes to allow the flavors to meld.

4. 4. Add the Tortellini: Increase the heat to medium and add the refrigerated tortellini to the simmering soup. Cook according to package directions, usually 3-5 minutes, until the tortellini are tender and float to the surface. Avoid overcooking, as they can become mushy.

5. 5. Stir in Cream and Spinach: Reduce the heat to low. Stir in the heavy cream until fully incorporated, giving the soup its rich, creamy texture. Add the fresh spinach and stir gently until it wilts, which should only take about 1-2 minutes.

6. 6. Taste and Serve: Taste the soup and adjust seasonings if necessary, adding more salt or pepper as desired. Ladle the hot soup into bowls and garnish generously with grated Parmesan cheese before serving.