Thaw the puff pastry overnight in the refrigerator or about 30 minutes at room temperature.
Combine the sugar and the kosher salt in a small mixing bowl, whisking to blend together.
Spread ½ cup of the sugar over a large surface. Place one sheet of the thawed puff pastry dough on top of the sugar. Cover the top of the pastry dough with another ½ cup of sugar, spreading it out as evenly as possible.
Gently roll the pastry dough out, pressing the sugar into the dough, smoothing out the folds and creating a sheet of dough that’s roughly about 13” x 13”.
Fold the left side of the dough halfway in towards the middle, then the right side in to meet the edge of the left side. Fold each side again to create a long narrow layered roll of dough.
Sprinkle an additional 2 tablespoons of dough onto the remaining sugar on the rolling surface. Place the second sheet of puff pastry dough on top of the sugar and spread a ½ cup of sugar evenly over the surface. Roll and fold in the same manner as the first sheet.
Spread the remaining 2 tablespoons of sugar over a sheet of parchment paper or cutting board.
Using a sharp knife, cut the pastry into ½” thick slices. Place the cookies on a Silpat or parchment paper lined baking sheet, leaving about 2” to 3” between each one.
Bake in a 425-degree oven for 16 to 18 minutes or until the palmiers are puffed and golden in color. If you want the sugar caramelized on both sides, flip the cookies halfway through the baking time.
Let the cookies cool slightly then transfer them to a wire rack to cool completely.