Place the milk, butter, salt and vanilla bean (pod) and seeds in a small saucepan over medium heat and bring to a boil, then immediately remove from the heat and let cool slightly.
Combine the sugar and flour in a mixing bowl.
Place the egg yolks in a separate bowl, then pour over the warm milk.
Add this to the flour and stir gently to combine, then stir in the rum. Cover and refrigerate for at least 24 hours and up to 48 hours before using, leaving the vanilla bean in the batter.
Preheat the oven to 400ºF (200ºC). To prepare new copper molds, brush with melted butter and beeswax and put in the oven for 1 hour, then let cool. If using silicone molds, place in the freezer for 1–2 hours before baking.
Increase the oven temperature to 425ºF (220ºC).
Remove the vanilla bean from the batter, then stir and transfer to a small bowl or jug. Lightly grease copper molds with butter. For silicone, use the melted butter and beeswax mixture.
Remove the vanilla bean from the batter, then stir and transfer to a small bowl or jug. Lightly grease copper molds with butter. For silicone, use the melted butter and beeswax mixture.
Pour the batter into the molds, leaving a 1/2 inch (1cm) gap at the top.
Place copper molds on a baking sheet and bake for 15 minutes, then lower the temperature to 400ºF (200ºC) and cook for another 15–20 minutes. If using silicone, set the oven to 475ºF (240ºC).
Bake for 25 minutes, then lower the temperature to 400ºF (200ºC) and bake for another 15–20 minutes.
Tap the molds to release the canelés.
Let cool completely on a wire rack and eat within a few hours of baking.
