Take the puff pastry sheets from the freezer and thaw as per package instructions. Make sure to check the package instructions as puff pastry brands vary from country to country. If you have a block of puff pastry, see note 1 for rolling instructions.
Preheat oven to 200°C or 400°F (180°C fan forced).
Use a pastry brush to lightly spread the whisked egg over the puff pastry sheet.
Sprinkle about 1/3rd of the sugar and nut mixture on the puff pastry sheet, making sure to cover it evenly. Use a rolling pin, a glass or just your hands to gently push the sugar and nut mixture into the puff pastry. This ensures that the sugar is pressed well into the puff pastry.
Fold the left and the right sides of the dough inward so they meet in the middle. Fold the left side over the right side, similar to closing a book. This will create a long, flat length of dough, with two folds in the middle.
Chill the dough in the freezer for about 10 minutes. This step can be skipped if the dough is firm enough. However, if the kitchen is too hot and the dough is sticky, this step will firm up the dough and make it easier to cut.
Repeat the process for the other two puff pastry sheets as well.
Once the palmiers are chilled, use a sharp serrated knife to slice the log into cookies that are about 1-inch wide.
Line a baking sheet with parchment/baking paper and place the cookies on the sheet. Sprinkle the palmiers with more sugar, if you want. Make sure to leave space between the palmiers as they will puff up.
Bake the palmiers, turning them halfway through, until crisp and golden, with the sugar turning into caramel during the baking process.
Remove the palmiers from the oven, and let them cool for a few minutes on the baking sheet. Transfer them to a cooling rack to cool completely. They will crisp up as they cool, and the sugar will harden as well. This recipe makes about 30 palmier cookies, and the serving size is 2 cookies per person.
Palmiers can be stored in an airtight container for a couple of days. However, they will begin to lose their crispness in a couple of days.
Freezer Instructions: Palmiers can only be frozen raw, not baked. Once you have cut the palmiers, line them on a baking sheet and freeze for about 3 – 4 hours. Once they are frozen, remove them from the baking sheet and store in an airtight container or freezer bag. Bake directly from frozen, adding 2 – 3 times to the normal baking time.
Instructions for Puff Pastry block:
In case have puff pastry blocks available instead of puff pastry sheets or you are using home-made puff pastry, you will need to roll the puff pastry into a square or rectangle to make palmiers. Start off with cutting the puff pastry block into 2 parts so that it’s easier to roll.
Spread a large sheet of baking paper on the work surface. This will help in preventing the dough from sticking to the work surface, and also help in moving it. With a rolling pin, roll out the puff pastry block in both directions to make a rectangle (roughly 10 x 15). Sprinkle flour on both sides in case the puff pastry sticks to the bottom. Do this with both puff pastry blocks. The method filling is the same as for puff pastry sheets. Baking time can vary if using a block of puff pastry. Make sure to read package instructions and adjust accordingly.