1. In a mixing bowl, combine mashed potatoes, milk, melted butter, sugar, and salt.
2. Sprinkle yeast over the mixture and let it sit for 5 minutes.
3. Gradually add flour, one cup at a time, until a soft dough forms.
4. Knead the dough on a floured surface for about 10 minutes.
5. Place the dough in a greased bowl, cover, and let it rise until doubled in size, about 1 hour.
6. Punch down the dough and shape it into a loaf. Place it in a greased loaf pan.
7. Cover and let it rise again until doubled, about 30 minutes.
8. Preheat the oven to 375°F (190°C). Bake for 35-40 minutes, or until golden brown.
9. Remove from the oven and let it cool on a wire rack before slicing.