Soak your vanilla bean in your rum overnight, or add your scrapped vanilla seeds to your rum the day of.
Preheat your oven to 375°F. Melt your butter and then allow it to return to room temperature, but still liquid.
Butter a 10” cake pan and line the bottom with parchment paper.
Mix flour, baking powder, and salt together in a medium bowl. Peel your apples and remove the core, then cut into a ½” dice.
Whisk your eggs until they get frothy, then whisk for another 2 minutes. Slowly add the sugar, whisking in until you have a nice smooth sugar egg cream. Add ⅔ your flour mixture, while stirring, until incorporated. Then add ½ your melted butter and whisk again. Now add your rum to the cake (removing the bean if you have chosen to soak the empty bean in the rum). Whisk in the rest of the flour and butter until you have what looks like a very thick pancake batter. Now fold in your apples until evenly distributed and pour into the cake pan. Smooth it down evenly and bake for 1 hour and 15 minutes. Test the cake at 1 hour to see how far it has come. A toothpick should come out clean from the center when it is done.
Remove from the oven and let cool for 5 minutes before using a plate to flip it out of the pan and then back onto a cutting board.