Using a dough hook, knead the dough with a stand mixer on medium-high speed for 5 minutes or until smooth. Add softened butter and constantly knead the dough at the same pace for 10 minutes or until smooth and elastic.
Transfer the dough to a floured surface, gently press the dough to release the air from it. Divide the dough into 16 equal portions and round each piece into a smooth ball.
Use a 9-inch square baking pan, place each dough onto the pan, half-inch apart. Lightly cover the dough with plastic wrap and rise for 30 minutes until puffy.