In a pot, bring the six cups of chicken stock to a simmer.
Meanwhile, in another pot, make the soffritto: heat the olive oil over medium-low and sauté the diced onion, carrot and celery for about 10 minutes until soft, stirring occasionally.
Add the potatoes, half the salt, and fry for a few minutes. Ladle enough stock to cover the potatoes, bring it to boil, reduce the heat to simmer, cover and cook the potatoes for 20 minutes or so until just tender.
Remove the lid, add another cup of stock and rest of the salt, increase the heat to bring to a boil, add the larger pieces of pasta and cook for 5-7 minutes until almost al dente, then add the smaller pieces of pasta and more stock if needed, then cook until al dente.
For a soupy texture, remove the pot from the heat, add the grated cheese and stir in well, and serve immediately. If you prefer more of a stew-like texture, continue to cook on low heat for another 5-10 minutes until the potatoes have broken down further and the pasta is soft, stir in the cheese and serve.
Drizzle on a little extra virgin olive oil, sprinkle on more grated cheese, and grind some fresh cracked black pepper on top.