Fold the top and the bottom of the dough over the butter so that they meet in the middle, covering the butter. Now fold the right and left edges of the dough into the middle. Fold the whole thing in half from right to left, so the seam ends up on the left. Press the dough firmly down to seal, and roll back out into a 12 x 16 inch rectangle. Repeat the folding process, then wrap tightly in plastic wrap and refrigerate for at least two hours or overnight.