Brown the sausage: Heat the olive oil in a large Dutch oven over medium-high heat. Add the Italian sausage and cook for 7-8 minutes, breaking it into small crumbles, until browned with no pink left and an internal temperature of 160°F. Leave it in the pot with the drippings.

Soften the vegetables: Add the onion and celery and cook for 4-5 minutes, stirring now and then, until the onion turns translucent and the celery loses its crunch.

Add the garlic and flour: Stir in the garlic, flour, Italian seasoning, and black pepper. Keep stirring for 1 minute, until the flour disappears into the fat and the pot smells like garlic instead of raw flour.

Simmer the broth: Pour in the chicken broth and the diced tomatoes with their juices, scraping the browned bits off the bottom. Bring it to a boil, then reduce to a steady simmer and cook uncovered for 10 minutes.

Cook the tortellini: Stir in the tortellini and simmer for 5 minutes, until they float and are tender all the way through. Check one before you move on, since package times vary by brand.

Finish with cream and spinach: Turn the heat to low. Stir in the heavy cream and the baby spinach and cook 2 minutes, until the spinach wilts and the soup is hot through. Don't let it boil again. Taste, then add the salt.

Serve: Ladle into bowls and top each one with grated parmesan.