Roll out the dough into a square and place the butter plate (without the baking paper) in the centre of the dough. Fold the corners of the dough around the butter plate to form an envelope.
First round: Carefully flatten the dough with a rolling pin* and roll out until you have an elongated rectangle. Fold in a third of the dough on the left-hand side and fold the right-hand third over it so that there are three equal layers of dough on top of each other.
Wrap the dough in a tea towel and place in the fridge for 30 minutes.
Then unwrap the dough again, carefully flatten with a rolling pin* and roll out into a long rectangle. For the second round, fold the rectangle in again to create three layers of dough.
Perform a total of three rounds. Place the dough in the fridge for 30 minutes between batches.
After the third round, the dough is rolled out into a large rectangle.
Cut the rectangle into twelve equal rectangles using a pizza cutter*. Place the chocolate on the short side of a rectangle and fold the edge over it. Place a second layer of chocolate on the edge and roll up the chocolate croissant.
Place the pain au chocolat on a baking tray, brush with milk, water or egg, cover and leave to rest for two to three hours - depending on the room temperature.
Brush the chocolate croissants again with milk or egg before baking.
Preheat the oven to 230 degrees using a steam tray consisting of a stainless steel oven dish* and lava stones*. Bake the pain au chocolat for 10 minutes with steam and about 20 minutes or until golden brown.