- In a medium bowl, combine the water, yeast, and ½ teaspoon sugar. Set aside to proof. 
- In the bowl of a stand mixer fitted with the hook attachment, add the remaining ⅓ cup of sugar, flour, mashed potatoes, salt, eggs, and butter. Turn the mixer on low until combined. 
- Slowly pour in the proofed yeast mixture and increase the mixer to medium. Continue on medium until a smooth dough forms and no longer sticks to the walls of the bowl. 
- Transfer dough to a large greased bowl and cover loosely with plastic wrap. Let rise for 90 minutes in a dark and warm environment, until doubled in size. 
- Spray a 9x13-inch baking pan with cooking spray. Divide and roll the dough into 16 balls, weighing about 85 grams each, and place in the greased baking pan, seam-side down. Cover loosely with plastic wrap and allow to rise for 2 hours in a dark and warm environment. 
- During the last 20 minutes, preheat oven to 350°F. Remove the plastic and bake for 20 to 25 minutes, until the tops are golden brown.