Place the warmed water, warmed leftover mashed potatoes, melted butter, sugar, salt, flour, and yeast into a bread machine pan in that order. Turn the bread machine to the dough setting and push start.
Once the dough cycle has completed (mine lasts 1½ hours).
Deflate the dough and turn it out onto a lightly floured surface. Form the dough into a roll and place into a loaf pan coated with cooking spray.
Cover with a cloth and let rise, until doubled in size, about 60 minutes.
Preheat the oven to 350 degrees. Place the loaf pan into the oven and bake for 35-40 minutes.
Remove from the oven and let cool for 10 minutes before putting on a cooling rack to continue cooling. Slice and serve slathered in butter. Enjoy.