Butter a 9-inch cast-iron skillet. Flour the work surface. Roll out the dough as thinly as possible, keeping a rectangular shape. Scatter 5 slices of the butter over two-thirds of the dough and sprinkle with 1/4 cup of the sugar. Fold the bare dough into the center and fold in the opposite side, like folding a letter. Dust with flour and roll out again as thinly as possible, retaining the rectangular shape. Top with another 5 slices of butter and 1/4 cup of sugar, folding, dusting with flour and rolling out the dough again as before. Repeat the process one last time, using the remaining 6 slices of butter and 1/4 cup of the sugar, folding and rolling it out as thinly as possible.