In a large mixing bowl, combine the mashed potatoes, warm milk, melted butter, sugar, and salt.
Sprinkle the yeast over the mixture and let it sit for 5 minutes until foamy.
Gradually add the flour, one cup at a time, mixing until a soft dough forms.
Turn the dough out onto a floured surface and knead for about 10 minutes, until smooth and elastic.
Place the dough in a greased bowl, cover, and let rise in a warm place for about 1 hour, or until doubled in size.
Preheat the oven to 375°F (190°C).
Punch down the dough and divide it into 12 equal pieces. Shape each piece into a roll and place on a greased baking sheet.
Cover the rolls and let them rise for another 30 minutes, or until doubled in size.
Bake in the preheated oven for 20-25 minutes, or until golden brown.
Remove from the oven and let cool on a wire rack.