1. Preheat the oven to 400°F.
2. Sprinkle half of the powdered sugar on the work surface.
3. Using a rolling pin, roll out the pastry into a rectangle of 20 x 30 cm. Sprinkle this rectangle with powdered sugar.
4. Fold the 2 large sides of the rectangle towards the middle. Sprinkle with sugar and fold the edges towards the middle again, leaving a half-centimeter space in the center.
5. Fold the pastry in half, rolling it to form a large bun.
6. Refrigerate for 30 minutes.
7. Cut the pastry bun into 1 cm thick slices. Brush with beaten egg yolks. Place the pieces on a baking sheet covered with parchment paper, leaving space between them.
8. Bake for 6 minutes.
9. Turn the palmiers over and cook for another 5 minutes.
10. Remove from the oven and serve immediately.