Heat the olive oil in a 5 to 6 quart pot over medium heat until it shimmers and moves easily when you tilt the pot, about 1 minute.

Add the onion, carrots, and celery. Cook, stirring every minute or two, for 7 minutes, until the onion is translucent and the carrots have lost their raw crunch.

Stir in the garlic, tomato paste, and Italian seasoning. Cook for 1 minute, stirring constantly, until the paste deepens to a brick red and the garlic is fragrant.

Add the broth, diced tomatoes with juices, bay leaf, Parmesan rind (if using), salt, and pepper. Raise the heat to high and bring to a boil, about 4 minutes, until large bubbles break across the surface.

Lower the heat to a gentle bubble and simmer for 7 minutes, until a piece of carrot slides off a fork with light pressure.

Add the tortellini and stir once. Cook for about 4 minutes, or the time on the package, until they float and one cut open is steaming hot in the center.

Add the spinach by the handful and cook for 1 minute, until wilted and bright green. Remove the bay leaf and Parmesan rind.

Stir in the lemon juice. Taste and add salt a pinch at a time until the broth tastes savory instead of flat.

Ladle into warm bowls, top each with 1 tablespoon of grated Parmesan, and serve right away while the tortellini are plump.