adapted from Katherine Burns @rue.dauphine.paris; makes one dozen full-sized canelés
Generously brush the mold interiors with melted butter. Cover pan with plastic wrap and place in freezer until ready to fill and bake.
In a saucepan, bring just to a gentle simmer the milk and vanilla bean. Immediately remove from heat, add the vanilla extract, cover, and let cool a few minutes. Remove the vanilla bean, scrape seeds, and return them to the milk.
Whisk the sugar and flour into the milk then add the egg yolks, melted butter, and rum. Strain into a glass 4-cup measure or bowl, cover with plastic wrap and refrigerate for at least 24 hours and up to 48 hours.
Preheat oven to 435°F. Whisk batter and pour into prepared molds, filling each about ¾ full. Bake for 15 minutes then lower heat to 375° and continue to bake for 40 minutes until the sides look dark and bubbly. Let cool for 10 minutes before tipping out onto a cooling rack. Rest canelés for 1 hour before eating so that the center sets. Bon Appétit!