Peel and grate potatoes. Pour off excess liquid. Combine yeast and warm milk, stir in sugar and set aside. Combine potatoes and salt in a mixing bowl. Gradually stir in flour and egg yolks. Add yeast mixture.
2
Beat egg whites until stiff and fold into potato mixture. Cover and let rise until doubled. Punch down and place in a greased loaf pan. Allow to rise again. Bake at 325 degrees for 1 hour. Remove from pan. When cool, cutbread into 1 inch thick slices and fry in melted butter until golden.