The broad beans from central Italy are the best in the world, and it is in this part of Italy that the best broad-bean dishes, such as this one, are made. Buy young, small beans with shiny pods.
Heat the oil in a saucepan and add the onion and the garlic. Fry gently until golden. Add the beans and the tomato purée and fry gently for 30 seconds, stirring all the time. Pour in the stock, add the bay leaf, stir and cook, covered, for about 10 minutes, until the beans are cooked. Taste and add the salt and pepper. Remove the bay leaf and discard it.