01 - Preheat the oven to 400°F (200°C) and line two baking sheets with parchment paper.
02 - Combine granulated sugar, ground cinnamon, and fine sea salt in a small bowl.
03 - Scatter half the cinnamon sugar evenly over the work surface. Place the puff pastry on top and gently roll to a 10 x 12 inch rectangle, pressing the dough into the sugar.
04 - Lightly brush the dough with melted butter if using, then sprinkle the remaining cinnamon sugar over the top, pressing gently to adhere.
05 - Starting from one long side, tightly roll the dough toward the center. Repeat with the other side so the rolls meet in the middle, forming a double-spiral log.
06 - Cut the log crosswise into 1/3 inch (about 1 cm) thick pieces, making approximately 24 slices. Arrange on prepared baking sheets, spacing well apart.
07 - Bake for 9 minutes. Flip each palmier with a thin spatula and continue baking for 8 to 9 minutes, until golden and caramelized.
08 - Transfer the pastries to a wire rack and allow to cool completely before serving.