Boil the beans and then mash them with the aid of a vegetable mill. In a casserole, pour in half of the oil and sauté the finely chopped onion, carrot and a stick of celery. As soon as the chopped mixture has become golden, add the tomato puree or a tablespoon of conserve. Season with a pinch of salt, add the bean puree and dilute with 2 ladlefuls of hot water. Bring back to the boil, then add the rice, taking care that the minestrone, when the cooking is finished, is fairly thick. Before serving, complete the dish, away from the heat, with the rest of the raw oil and some grated Parmesan.