In a small saucepan, heat milk and vanilla bean paste over medium-low heat, stirring frequently, just until bubbles form around sides of pan. (Do not boil.)

In a medium bowl, whisk together sugar, egg yolks, melted butter, and salt. Gradually add half of hot milk mixture, whisking constantly. Whisk in flour until smooth; whisk in remaining hot milk mixture. Whisk in rum. Strain batter through a fine-mesh sieve into an airtight container. Cover with plastic wrap, pressing wrap directly onto surface of batter to prevent a skin from forming. Cover with lid, and refrigerate for at least 48 hours or up to 4 days.

Preheat oven to 450°F (230°C). Line a rimmed baking sheet with foil. Place a wire rack on another rimmed baking sheet. On foil-lined pan, place 6 seasoned canelé molds, and preheat in oven for 5 to 10 minutes. Leave oven on.

In a microwave-safe liquid-measuring cup, heat clarified butter and beeswax on high in 30-second intervals, stirring between each, until completely melted and combined.

Wearing heatproof gloves or using a cloth to protect your hands, fill 1 hot canelé mold halfway with beeswax mixture; swirl and coat entire inside, and pour excess mixture back into bowl. Place mold, upside down, on prepared rack, letting excess beeswax mixture drip from mold for 30 seconds to 1 minute. Repeat with remaining molds. Repeat procedure one more time with all molds. Let beeswax mixture harden at room temperature, or refrigerate for 10 to 15 minutes to speed up the process.

Gently stir batter with a spoon or silicone spatula to emulsify. (Do not whisk; you do not want to introduce more air.) On foil-lined prepared pan, divide batter among canelé molds, leaving about 3/8 inch of space at top to allow for rising. (In molds we used, it’s about 1⁄4 cup or 75 grams per mold.)

Bake for 20 minutes. Rotate pan, and reduce oven temperature to 350°F (180°C). Bake until top and outside of canelés are deep golden brown, 45 to 55 minutes more, rotating pan again after 20 minutes of baking. Carefully remove 1 canelé from mold; if it does not have a uniform color, return it to mold, and bake for 5 to 10 minutes more. Immediately invert canelés onto a wire rack, and let cool completely. Best served same day as made.