In a bowl, mix the sugar with the cinnamon. On a lightly floured work surface, roll out the dough to a 12-by-18-inch rectangle. Spread the butter over the dough, leaving a 1-inch border all around. Sprinkle the dough with the cinnamon sugar. Starting at a long side, roll the dough into a log and turn it seam side down. Cut the dough into 12 slices. Arrange the slices, cut side up, in the baking dish. Cover and let stand in a warm place until the buns double in volume, about 1 hour.