Boil until tender in water to cover:
3 or 4 medium russet potatoes, pared and cut into chunks
Drain, reserving potato water and mash potatoes well. Allow to cool to room temperature.
In the bowl of a stand mixer or in a large mixing bowl, combine:
1 ½ cups of the mashed potato, cooled
1 ½ cups potato water, cooled
2 tablespoons sugar
2 teaspoons salt
½ cup butter, softened
In a medium bowl, stir together:
5 cups freshly ground hard white wheat flour (you will need additional flour while kneading)
¼ cup powdered milk
2 ½ teaspoons instant yeast (also called bread machine yeast)
Add flour mixture to potato mixture, mixing gradually until well-combined and then kneading until the gluten is fully developed (it should pass the window pane test), adding additional flour as necessary to keep from sticking. Place in a large greased or oil-sprayed bowl and let rise until doubled in bulk. Turn out and fold as above and let rise until doubled again. Divide into 2 pieces, round, rest and shape into loaves. Alternately, divide into six equal pieces and make two braided loaves. Place in pans (or onto cookie sheets for braids), cover and let rise until doubled. Preheat oven to 400 degrees. Bake at 400 degrees for 10 minutes, turn heat down to 350 degrees and bake 30 to 35 minutes longer. Cool on a wire rack.