Unroll the puff pastry and cut into about 5 pieces of cake. Place the chocolate bars on the long side and roll up the puff pastry towards the tip.
Whisk the egg and brush the croissants with it. Bake the croissants on a baking sheet lined with baking paper in a preheated oven at 180 ° C for about 15-20 minutes until they are golden brown.