Thaw puff pastry in the fridge until pliable but still cold, or make my easy rough puff pastry.
Line 2 baking sheets with parchment paper; there's no need to grease them, as the puff pastry contains enough fat.
Dust your work surface with sugar, not flour. Lay the pastry on top and sprinkle more sugar over the surface. Roll lightly with a rolling pin to press the sugar into both sides.
Shape using one of two methods. Fold method: fold both long edges inward to meet in the center, leaving a small gap; fold inward again, then fold one half over the other like closing a book. Roll method: roll both short edges tightly toward the center until they meet in the middle. Keep folds tight throughout.
Wrap the shaped log and freeze it for at least 20 to 30 minutes.
Preheat oven to 200°C / 390°F (no fan).
Slice the chilled log into 1 cm / ½ inch pieces using a sharp knife with a single confident cut. One by one, dip each slice into the remaining sugar on the work surface to coat, then place cut-side up on a parchment-lined baking sheet with plenty of space between each cookie.
Bake the cold dough at 200°C / 390°F (no fan) for 12 to 15 minutes or until the base is bubbling and caramelized. Flip and bake for a further 8 to 10 minutes until deep golden brown. Check the base color before removing from the oven.
Cool on the tray for 5 minutes, then transfer to a wire rack. They will crisp up as they cool.
Store in an airtight container at room temperature for up to 3 days. To make ahead, freeze raw slices and bake straight from frozen, adding 2 to 3 minutes per side.
Notes
If the pastry softens at any point during the rolling or folding, return it to the fridge for a few minutes before continuing.
Check the bottom of the pastry - whether it is well baked - before taking the Palmiers out of the oven
Try this palmiers recipe with cinnamon sugar for a lovely cinnamon palmiers