Soak the dried beans in cold water overnight. Drain and drain well.
Heat the butter in a saucepan and sauté the onions and garlic. Reduce the heat and add the beans. Pour in the broth and cover and let everything simmer for about 1 hour. Stir every now and then and add a little more stock if necessary. When the beans are done, transfer them to a bowl and add the dressing. Mix everything well and let it steep for about 30 minutes.
Before serving, mix in the parsley and sprinkle with the bacon and walnuts.