Sprinkle half of the sugar evenly over a clean work surface. This sugar replaces flour and ensures the pastry absorbs sweetness at every layer.

Place the puff pastry sheet on top of the sugar. Sprinkle the remaining sugar evenly over the top. Using a rolling pin, gently roll the pastry into a rectangle about 10 by 14 inches. Press lightly so the sugar adheres to the pastry.

Starting from one long side, fold the pastry inward toward the center, stopping halfway. Repeat on the opposite side so the two folds meet in the middle. Then fold one half over the other, like closing a book. You should have a long, compact log with visible layers.

Wrap the folded pastry in parchment paper or plastic wrap and refrigerate for at least 30 minutes. This step helps the cookies hold their shape and ensures clean slices.

Preheat the oven to 400°F. Line two baking sheets with parchment paper. Using a sharp knife, slice the chilled pastry into pieces about 1/4 to 1/2 inch thick. Lay the slices flat on the baking sheets, leaving space between each one for spreading.

Bake for 5 to 6 minutes, then carefully flip each palmier using a spatula. Return to the oven and bake for another 5 to 6 minutes, until deeply golden and crisp on both sides.

Transfer the palmiers to a wire rack to cool. They will continue to crisp as they cool, and the caramelized sugar will set into a delicate crunch.