Combine ½ cup of the sugar and kosher salt and pour it over a flat surface such as a wooden board or marble slab. Unfold the sheet of puff pastry onto the sugar mixture.
Combine ½ cup of the sugar and the cinnamon and spread it evenly on the puff pastry. This is not about sprinkling, it's about an even covering of sugar. With a rolling pin, lightly roll the dough until it's a 13-inch square and the sugar is pressed into the puff pastry on top and bottom. Fold the sides of the square toward the center so they go halfway to the middle. Fold them again so the two folds meet exactly at the middle of the dough. Then fold one half over the other half as though closing a book. You will have 6 layers. Slice the dough into 3/8-inch slices and place the slices, cut side up, on baking sheets lined with parchment paper.
Bake the cookies for 6 minutes, or until caramelized and brown on the bottom, then turn with a spatula and bake for another 3 to 5 minutes, until caramelized on the other side. Transfer to a baking rack to cool.