Peel and cook the potatoes for about 30 minutes or until tender, drain them and save the water. Mash the hot potatoes, adding the salt, sugar and butter and beat well; add the potato water and hot milk and cool until lukewarm. Add the yeast and stir in 4 cups of the flour, beating well; then add enough of the remaining flour to make a dough stiff enough to knead. Knead on a floured board until smooth and elastic; brush the top with more melted. butter and place in a large greased bowl; cover and let rise slowly for 5 hours in a warm place until the dough has doubled in bulk. Place on a floured board and pat out to a thickness of about ½ inch, but do not knead again. Pinch off small pieces and shape into small rolls. Place them in greased pans and let rise until very light and more than doubled in bulk. Bake in a hot (400 degrees F) oven for 20 minutes or until done.