Mix together the butter, milk and salt in a saucepan.
Bring the milk, mixed with the vanilla powder and vanilla essence, to just before the boil. Remove the saucepan from the heat and allow it to cool.
Measure out the flour and icing sugar and sieve them into a bowl.
Carefully beat the eggs and the yolks with a fork.
Add the eggs to the flour and sugar mixture and mix the milk mixture in a little at a time, using a rubber spatula. Sieve the mixture if it becomes a little lumpy.
Add the rum, and the orange zest and mix together.
Cover the bowl with cling film and refrigerate for at least 24 hours.
Preheat the oven to 250°C. Melt the butter and beeswax for the tins on a low heat in a saucepan and preheat the tins briefly in the oven (otherwise there'll be too much beeswax on the sides). Fill the first tin with the beeswax mixture, making sure to cover it fully, then pour the mixture into the next tin and so on... turn the tins upside down, letting them drip a little, and then refrigerate for 10 minutes.
Pour the mixture into the tins, leaving 5 mm at the top.
Place the baking trays in the oven and lower the temperature to 175°C.
Bake for 60−90 minutes. Remove one canelé from the oven and release it from the tin. If it looks too pale, leave the remaining canelés in the oven a little longer. The canelés should be golden on the outside and slightly creamy in the centre. Remove all of the canelés from the oven and release them from the tins. Spread them wide apart so you don't destroy the crisp outsides.