Grease a 9 x 13-inch baking pan with butter. Unroll the first roll of phyllo pastry sheets. Lay two sheets of phyllo in the bottom of the pan. Lightly brush the top layer with melted butter. Add two more sheets and brush the top with butter. Continue adding sheets two at a time until you've laid down a total of 18. (You may want to keep the pastry covered with a damp paper towel prevent them from drying out.).