1. Preheat your oven to 375°F (190°C).

2. Line a baking sheet with parchment paper.

3. Roll out the puff pastry on a lightly floured surface until it reaches a thickness of about 1/8 inch (3 mm).

4. Spread the Nutella evenly over the center of the pastry, making sure to leave a 1-inch (2.5 cm) border around the edges.

5. Sprinkle the chopped dark chocolate and almond flour over the Nutella, distributing them evenly.

6. Fold the 1-inch border over the filling, then roll the pastry into a tight log.

7. Cut the log into 8 equal pieces, making sure each piece is roughly the same size.

8. Place the rolls seam-side down on the prepared baking sheet, leaving about 1 inch (2.5 cm) of space between each roll.

9. Brush the tops with the beaten egg and sprinkle with almond slices.

10. Bake in the preheated oven for 20-25 minutes, or until the rolls have turned golden brown.

11. Allow the rolls to cool on a wire rack before serving.