1. Heat the olive oil in a large pot or Dutch oven over medium heat. Add the Italian sausage, breaking it up with a spoon as it cooks. Continue cooking until the sausage is nicely browned and no longer pink, about 5-7 minutes. Once cooked, drain any excess grease from the pot.

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

3. Pour in the chicken broth, diced tomatoes (undrained), and tomato paste. Stir well to combine, ensuring the tomato paste is fully incorporated into the liquid. Add the dried Italian seasoning, salt, and black pepper. Bring the mixture to a gentle simmer.

4. Once the soup is simmering, add the refrigerated cheese tortellini to the pot. Cook according to the package directions, typically 3-5 minutes, until the tortellini are tender and float to the surface. Avoid overcooking, as they can become mushy.

5. Reduce the heat to low. Stir in the heavy cream until the soup takes on a lovely, creamy consistency. Then, add the fresh spinach, stirring gently until it wilts into the soup, which usually takes just a minute or two.

6. Remove the soup from the heat. Stir in the grated Parmesan cheese until it melts and thickens the soup slightly. Taste and adjust seasonings if necessary. Ladle the warm soup into bowls and serve immediately, topped with extra Parmesan cheese if desired.