01 - Set oven temperature to 400°F. Line two baking sheets with parchment paper.
02 - In a small bowl, blend granulated sugar, ground cinnamon, and sea salt if using.
03 - Sprinkle half of the cinnamon sugar mixture evenly over your work surface. Lay the puff pastry sheet on top.
04 - Sprinkle the remaining cinnamon sugar evenly over the pastry. Gently roll the pastry into a 10x12-inch rectangle using a rolling pin, embedding the sugar mixture.
05 - Roll the pastry tightly from one long edge toward the center. Repeat with the opposite edge so both rolls meet in the middle, creating a double spiral.
06 - Slice the rolled pastry crosswise into 1/2-inch thick pieces, yielding approximately 24 slices.
07 - Place slices cut side up on the prepared sheets, spacing well apart. Lightly sprinkle with extra granulated sugar.
08 - Bake for 8 to 10 minutes. Flip each palmier and bake for an additional 7 to 8 minutes until golden and caramelized.
09 - Allow to cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.