1. Bring milk and vanilla bean seeds to a boil.
2. Meanwhile, place the flour and powdered sugar in a large mixing bowl. Whisk together the eggs and egg yolks and pour over the dry ingredients, then add the soft Plugrá Butter.
3. Remove the boiling milk from heat and pour into the mixing bowl. Combine using an immersion blender until the mixture has a smooth texture. If you do not have an immersion blender you can use a hand mixer at medium speed or a whisk.
4. Place the mixture in the refrigerator and chill overnight. After chilling, whisk in the rum and chill overnight again.
5. Preheat a conventional oven to 400°F.
6. Bring cake mixture to room temperature. Whisk the mixture well.
7. Fill the molds to ¼ inch below the top of the mold and place on a sheet pan. Place sheet pan in the preheated oven and bake for approximately 1 ½ hours. Check one of the molds after 1 ½ hours of baking, the cake should pop cleanly out of the mold. If they resist, bake them a little longer.

Chef's Note: The cake batter is best used three days after it is made.