Cut up the puff pastry into 3 parts. Roll out each one carefully. Before putting them in the oven, pierce them in several places with a fork.
Bake to a golden tan in a 392°F (200°C) oven in a tray sprinkled with cold water. Remove from the oven and let them cool.
Prepare a fluffy cream by mixing the powdered sugar with the cream. Add the vanilla and grated chocolate and stir.
Smear this cream on the puff pastry layers. Smear the top of the cake with cream and sprinkle with cocoa.