In a large dutch oven or pot, add the olive oil and the finely diced carrots, celery, and onion. Cook for 3-4 minutes or until fragrant.
In the pot, pour the crushed tomatoes and the beans.
Add salt and pepper, then add in the baby spinach.
Mix the ingredients together, then pour in the vegetable stock. Mix again to fully combine.
Last, add in the parmesan rind. Close the lid and bring the heat to a low or simmer for 2 hours, stirring occasionally.
15-20 minutes before the soup is done, pour in the ditalini and stir. Close the lid and simmer for the remainder of time. Plate and garnish with fresh grated parmesan.
Notes
The more liquid you start with, the better. The reason for this is because the starch from the beans and from the ditalini cooking in the soup, it'll absorb the liquid and make it thicker. This is meant to be a thick soup, but it should also have some liquid.