Method
Prep:30min  ›  Cook:40min  ›  Ready in:1hr10min 

1. In a medium saucepan, cook potato in water for about 12 minutes, or until tender. Do not drain. Cool mixture to 43 C. Set aside 125ml of the cooking liquid. Mash potato and remaining liquid; if necessary add warm water to make 500ml potato mixture.
2. In a large mixing bowl, sprinkle yeast on reserved 125ml potato water. Add mashed potato mixture, 2/3 of the flour, sugar, butter and salt. Beat with an electric mixer on low speed for a minute, scraping sides of bowl constantly. Beat 3 minutes at high speed. Stir in as much of the remaining flour as you can, mixing in by hand.
3. Turn dough out onto a lightly floured surface. Knead in enough of the remaining flour to make a moderately stiff dough. Knead for 6 to 8 minutes, or until dough is smooth and elastic. Place in a lightly oiled bowl; turn once to coat surface. Cover. Let rise in warm place until doubled in bulk, about 1 hour.
4. Punch down, and turn out onto a lightly floured surface. Divide dough in half. Cover, and let rest for 10 minutes. Shape each half into a loaf. Place in greased loaf tins. Cover. Let rise until nearly double, about 35 minutes. Before baking, brush tops with a little water and dust with additional flour.
5. Bake at 190 C / Gas mark 5 for 40 to 45 minutes. Cover with aluminium foil for the last 15 minutes of baking to prevent over-browning. Remove from tins; cool on wire rack.