Preheat the oven to 450°.  Line two large baking sheets with parchment paper and set aside.

Mix the sugar and salt together in a small bowl.  Sprinkle 1/2 of the sugar on a marble or wood surface large enough to roll out the puff pastry.  Unfold the sheet of puff pastry on top of the sugar, ensuring the sugar covers and is pressed into the bottom of the dough.  Sprinkle the remaining sugar on top of the puff pastry, spreading it to evenly cover with the back of a spoon.  Roll the puff pastry into a 14 x 14-inch square, ensuring the sugar is pressed into the surface of the dough.  Brush off the excess sugar; you may not use all of the sugar, but make sure the dough is evenly covered.  Fold each side of the dough onto itself, halfway to the center.  Repeat the fold to bring the two folded pieces to meet in the center.  Fold a final time so one half of the dough is on top of the other half, as if you’re closing a book.  You will have a total of 6 layers.  Press the dough down lightly to seal.  Cut into 1/4-inch-thick slices and place on the prepared baking sheets, leaving some space between each cookie to allow them to “puff” (pastry, duh).

Bake one sheet of cookies at a time to ensure even browning.  Place the second sheet in the refrigerator until ready to bake.  Bake each sheet for 6 to 7 minutes, until the tops are golden and the sugar is caramelized.  Remove from the oven and allow to sit for 2 minutes before flipping.  Return the cookies to the oven to bake for an additional 3 to 6 minutes, until golden brown and caramelized on the second side.  Allow to set on the baking sheet for 2 minutes before removing to cool on a cooling rack.  Repeat with the second baking sheet.