Thaw frozen puff pastry according to package instructions.
Preheat oven to 180 C / 350 F. Line a baking tray with baking paper.
Break the chocolate bar into sections. Set aside.
Lay puff pastry sheet on a flat surface and cut into 6 rectangles.
Place the chocolate in the center of each rectangle.
From the short end, roll up each rectangle and press down lightly to seal the edges.
Transfer to a baking sheet.
Brush tops and sides with whisked egg.
Bake for about 20 minutes or until the pastries are golden.
These are best served warm out of the oven.
Dust with powdered (icing) sugar if you like.