Place cold puff pastry on a floured surface and roll it out to about 10 by 12 inches. Brush melted butter evenly over the entire surface, then sprinkle the sugar-cinnamon mixture evenly over the pastry. Press gently with a rolling pin so the sugar sticks well.
1 sheet puff pastry, 2 tablespoons butter, 0.5 cup granulated sugar, 1 tablespoon ground cinnamon
Fold both long edges of the dough toward the center so they meet in the middle, then fold in half again like closing a book. You will have a narrow log shape with multiple visible layers at the ends.
1 sheet puff pastry
Wrap the dough log tightly in plastic wrap and refrigerate it for 30 minutes. This chilling step ensures the dough slices cleanly without compressing the layers.
Use a sharp knife or dental floss to cut the chilled dough log into ¼-inch thick slices. Place the slices flat on a parchment-lined baking sheet spaced about 2 inches apart to allow spreading during baking.
Bake the slices in a preheated oven at 400°F for 12 to 15 minutes, rotating the pan halfway through baking. The palmiers are done when the edges turn golden brown and the sugar bubbles and caramelizes. Let cool on a wire rack for 5 minutes before serving.
