Purgatory beans with fresh onion

Preparation: Finely chop the onion and sauté it in a bowl with salt and vinegar. Meanwhile, cook the purgatory beans for about an hour, without soaking them. Drain them and then add the onion. Season with extra virgin olive oil, salt, and pepper. These beans are used in the famous "Pranzo del Purgatorio," a banquet held in Gradoli every year on Ash Wednesday.