First make leaven with all ingredients and set aside for 6 hours.

Mix, flour, leaven, salt, sugar, milk powder, potato flour, milk, water and butter and form a shaggy dough.

Fold the dough every 30 minutes for first 2 hour and then 1-hour interval for next two hours. Finally, after 6 hours.

Line 16-inch round pizza pan with parchment paper; place 3 ½-inch diameter bowl upside down in center of pan. Punch down dough. Divide dough evenly into 25 pieces of 42 g. Shape 1 piece into ball, folding ends underneath and pinching at bottom; roll on work surface in circular motion, seam side down, into smooth ball. Repeat with remaining dough pieces.

Arrange balls in ring shape around bowl; place 10 balls first row and 15 balls around first layer. Cover with plastic wrap; let rise in warm draft-free place until doubled in size, or refrigerate the dough for overnight.

Preheat oven to 375°F. Bake until rolls are golden and sound hollow when tapped, 37 minutes. Brush with butter. Let cool for 10 minutes before serving.