Cut butter into 4 rectangles.

Fold a 24x8-inch sheet of parchment paper in half to create a 12x8-inch rectangle. Unfold parchment, and place butter on one side. Pull other half of parchment over butter. Using a rolling pin, pound butter into an 11x7-inch rectangle. (Try not to roll butter, as it creates friction and heat. You want it o stay as cold as possible.) Freeze for 5 minutes; refrigerate until ready to use. (This can be made a day ahead.)