Rinse the soaked chickpeas, cover with water, add the potato, and cook with until tender, about 1 hour.

In a large pot, heat the olive oil and butter. Add the leeks and garlic with a pinch of salt and sautee until tender.

Add the chickpeas and potato and cook for 1 minute. Add about two-thirds of the stock and simmer for 15 minutes.

Puree half the soup in food processor. Add remaining stock. Season with salt, black pepper and add grated Parmesan cheese.

Ladle soup into serving bowls, drizzle with some olive oil, add ground black pepper, some more Parmesan cheese and serve.