Sauté the chopped shallot in a drizzle of extra virgin olive oil in a large saucepan; add the chickpeas, cubed potatoes, chestnuts and rosemary.
Add the hot broth and cook for 20 minutes, until the potatoes are soft.
Remove from the heat, add the grated Grana Padano Riserva, season with salt and pepper and purée using an immersion blender.
Crumble the sausage and brown it for a few minutes in a non-stick pan.