How to Make It
Stir together all-purpose flour, potato flour, milk powder, sugar, salt, and yeast in a medium bowl; set aside. Combine 1 cup warm water and 1/4 cup melted butter in bowl of a stand mixer fitted with the dough hook attachment. With mixer running on low speed, gradually add flour mixture to butter mixture, beating until incorporated, about 3 minutes. Increase speed to medium-low, and beat until dough becomes smooth and elastic, about 6 minutes. (Dough will be sticky.) Transfer dough to a large bowl lightly coated with cooking spray. Cover with plastic wrap; let stand at room temperature until doubled in size, 45 minutes to 1 hour.
Turn dough out onto a lightly floured work surface. Divide dough evenly into 8 portions (about 31/8 ounces each); shape each dough portion into a ball. Arrange dough balls at least 2 inches apart on a baking sheet lined with parchment paper. Flatten each ball into a 3-inch-wide round (about 3/4 inch tall). Cover loosely with plastic wrap; let stand at room temperature until rounds are puffy and doubled in size, 35 to 45 minutes.
Preheat oven to 350°F. Gently remove and discard plastic wrap from dough rounds. Bake dough rounds in preheated oven until golden brown, 14 to 18 minutes. Transfer hot rolls to a wire rack; immediately brush tops and sides of rolls with remaining 1 tablespoon melted butter. Let rolls cool completely, about 30 minutes.