Split the vanilla pod and roughly break the cinnamon stick, and place in a medium saucepan with the milk and cream.
Slowly bring the cream mixture to the boil over a medium heat, then immediately remove from the heat.
Place a lid on the saucepan and set aside to infuse for 30 minutes.
In a separate bowl, whisk the egg and castor sugar together until frothy.
Sieve the infused cream mixture into the beaten egg, add the ground nutmeg and whisk together.
Grease a 21cm x 28cm x 8cm baking dish with butter.
Split the croissants and place a layer in the bottom of the baking dish.
Scatter half of the chopped chocolate over the croissants.
Place the remainder of the croissants over the chocolate and scatter the remaining chocolate over the top of the dish.
Gently pour the custard over the croissants, ensuring that they are evenly covered. Press the croissants under the custard if necessary.
Set the baking dish aside for 30 minutes to allow the custard to be absorbed.
Pre-heat the oven to 180C (160C fan forced).
Bake the pudding for approximately 30 minutes, until it is puffed and golden, and the chocolate is melted.
Allow to stand for 5 - 10 minutes before serving, if you can wait that long.