1. Heat the olive oil in a large pot or Dutch oven over medium-high heat. Add the Italian sausage (casings removed if using links) and break it up with a spoon. Cook until the sausage is fully browned and no longer pink, about 5-7 minutes. Drain off any excess grease from the pot.

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

3. Pour in the chicken broth, diced tomatoes (undrained), and tomato paste. Stir well to combine, ensuring the tomato paste is fully dissolved into the liquid. Add the dried basil, dried oregano, and red pepper flakes (if using). Bring the mixture to a gentle boil, then reduce the heat to a simmer.

4. Let the soup simmer for 10-15 minutes, allowing all the flavors to meld together beautifully.

5. Add the refrigerated cheese tortellini to the simmering soup. Cook according to package directions, which is usually about 3-5 minutes, until the tortellini is tender but still firm to the bite (al dente).

6. Stir in the heavy cream and fresh spinach. Cook for just 1-2 minutes more, or until the spinach has wilted.

7. Taste the soup and season generously with salt and black pepper as needed. Ladle the hot soup into bowls and garnish with grated Parmesan cheese before serving.