Roll 1 pastry sheet into a 13- x11-inch rectangle. Stir together butter, and salt. Brush half of butter mixture over pastry. Sprinkle with half of chili powder and cilantro.
Roll up pastry, jellyroll fashion, starting with each short side and ending at middle of pastry sheet. Repeat procedure with remaining pastry sheet, butter mixture, chili powder, and cilantro.
Cut rolls crosswise into 1/3-inch-thick slices. Place on a lightly greased baking sheets. Whisk together egg yolk and 1 tablespoon water, and brush evenly over pastries.
Bake at 375º for 10 to 15 minutes or until golden brown.