Heat the milk and butter. Add the vanilla and cool.
In a large bowl whisk the sugars, 1 to 1 flour, tapioca, cornstarch, eggs, egg yolks, and rum. Stir gently. Add in cooled milk and butter mixture. Whisk until fluffy and mixed. Refrigerate for 8 hours or overnight.
Bring to room temperature 4-5 hours before planning to bake. Pour the batter into a room temperature bowl.
When the batter is nearly room temperature, melt the 50 gr (3 tbsp) butter. Brush each hole of the mold with butter using a pastry brush. Freeze the mold tray for 35-40 minutes.
Preheat the oven to 450℉ with the rack in the center of the oven when the 45 minutes is nearly up. Remove the tray from the refrigerator. Stir the batter gently a few times. Pour the batter in using a measuring cup and filling to about ⅜" from the top. Immediately move to the preheated oven and bake for 15 minutes. Turn the oven down to 360℉ and bake for 45 minutes, turning the pan or pans in the oven, without removing them.
Remove from the oven. Let sit for 5-10 minutes. Invert the canelé carefully to a parchment piece set over a wire rack until cool enough to handle.
Then set the canelé directly on the rack to cool. When cooled for one to one and a half hours, move the canelé to an airtight container.
* Note: to recrisp any remaining canelé after a day or two, preheat the oven to 350℉. Set the canelé on a baking sheet. Put in the preheated oven for 12-15 minutes or until crisp on the exterior. Let cool completely before serving.