Drain and rinse the chickpeas. Finely dice the onion and celery, and peel and cut the potato into chunks. In a large heavy-based pan, warm the olive oil, add the onion and celery and cook gently until soft and fragrant.
Add the potato and stir until each chunk glistens, then add the rosemary, tomato and chilli (if you are using it), stir and cook for a minute before adding the chickpeas. Add 1.2 litres of water, a pinch of salt and the parmesan rind if you are using it.
Bring to the boil, then reduce to a gentle simmer for 20 minutes.
Taste and add more salt if necessary. Bring the soup to a steady but moderate boil, add the pasta and then – stirring pretty attentively – cook until the pasta is tender, adding a little more water if necessary. Taste to check seasoning, adding black pepper if you wish. Serve with a little more olive oil poured over the top.
