01 - Set the oven to 400°F. Line two baking sheets with parchment paper.
02 - In a small bowl, thoroughly mix granulated sugar, ground cinnamon, and optional sea salt.
03 - Evenly sprinkle half the cinnamon sugar mixture over the work surface. Place the puff pastry sheet on top.
04 - Sprinkle the remaining cinnamon sugar evenly over the puff pastry. Using a rolling pin, gently roll the pastry into a 10x12 inch rectangle, pressing the sugar into the surface.
05 - Starting from one long edge, roll the pastry tightly toward the center. Repeat from the opposite edge so the two rolls meet in the middle, creating a double spiral.
06 - Slice the double-rolled pastry crosswise into 1/2-inch thick pieces, producing about 24 slices.
07 - Place the slices cut side up on prepared baking sheets, spacing well apart. Lightly sprinkle with extra granulated sugar.
08 - Bake for 8 to 10 minutes. Carefully flip each palmier and bake for an additional 7 to 8 minutes until golden and caramelized.
09 - Allow palmiers to cool on baking sheets for 5 minutes, then transfer to a wire rack to cool fully before serving.