In a large mixing bowl, combine the warm water, sugar, and vegetable oil. Sprinkle the active dry yeast over the top and let it sit for about 5 minutes until it becomes frothy.
Add the mashed potatoes, egg, and salt. Stir until well combined.
Add the nonfat dry milk powder and 3 cups of all-purpose flour to the mixture. Stir until a dough begins to form. Gradually add 2-1/2 to 3 cups of bread flour, 1/2 cup at a time, until the dough pulls away from the sides of the bowl and is no longer sticky.
Turn the dough out onto a floured surface and knead for about 5-7 minutes until it is smooth and elastic. Form it into a ball and place it in a greased bowl, turning it to coat with oil.
Cover the bowl with plastic wrap or a clean kitchen towel and let it rise in a warm place for about 1 hour, or until it has doubled in size.
While the dough is rising, mix together the room temperature butter, brown sugar, and cinnamon in a small bowl until it forms a smooth paste.
Once the dough has risen, punch it down to release the air. Turn it out onto a floured surface and roll it into a 16x24-inch rectangle.
Spread the cinnamon filling evenly over the rolled-out dough, leaving a small border around the edges.
Starting from the long side, carefully roll the dough into a tight log. Pinch the seams to seal.
Using a sharp knife or dental floss, slice the log into 12 equal pieces. Place the rolls in a greased baking dish, cut side up.
Cover the rolls with plastic wrap or a towel and let them rise for another 30-45 minutes until puffy.
Preheat your oven to 350°F (175°C). Bake the rolls for 25-30 minutes, or until golden brown and cooked through.
Allow the rolls to cool in the pan for 10 minutes before serving. Drizzle with your favorite icing if desired.