Unfold pastry onto a lightly floured 20-inch long sheet of waxed paper. Roll into a 9- by 15-inch rectangle using a floured rolling pin. Spread filling down center of pastry sheet. Fold pastry over filling, folding short sides in first, then fold over the 2 large sides, envelope style. Pinch seams closed. Place seam-side down onto prepared baking sheet. Remove waxed paper. Brush with melted butter.